10.4. Unauthenticated ciphers

Warning

The unauthenticated cipher API is provided to implement legacy protocols and for use cases where the data integrity and authenticity is guaranteed by non-cryptographic means.

It is recommended that newer protocols use Authenticated encryption with associated data (AEAD).

The single-part functions for encrypting or decrypting a message using an unauthenticated symmetric cipher are:

  • psa_cipher_encrypt() to encrypt a message using an unauthenticated symmetric cipher. The encryption function generates a random initialization vector (IV). Use the multi-part API to provide a deterministic IV: this is not secure in general, but can be secure in some conditions that depend on the algorithm.

  • psa_cipher_decrypt() to decrypt a message using an unauthenticated symmetric cipher.

The psa_cipher_operation_t multi-part operation permits alternative initialization parameters and allows messages to be processed in fragments. A multi-part cipher operation is used as follows:

  1. Initialize the psa_cipher_operation_t object to zero, or by assigning the value of the associated macro PSA_CIPHER_OPERATION_INIT.

  2. Call psa_cipher_encrypt_setup() or psa_cipher_decrypt_setup() to specify the algorithm and key.

  3. Provide additional parameters:

    • When encrypting data, generate or set an IV, nonce, or similar initial value such as an initial counter value. To generate a random IV, which is recommended in most protocols, call psa_cipher_generate_iv(). To set the IV, call psa_cipher_set_iv().

    • When decrypting, set the IV or nonce. To set the IV, call psa_cipher_set_iv().

  4. Call the psa_cipher_update() function on successive chunks of the message.

  5. Call psa_cipher_finish() to complete the operation and return any final output.

To abort the operation or recover from an error, call psa_cipher_abort().

10.4.1. Cipher algorithms

PSA_ALG_STREAM_CIPHER (macro)

The stream cipher mode of a stream cipher algorithm.

#define PSA_ALG_STREAM_CIPHER ((psa_algorithm_t)0x04800100)

The underlying stream cipher is determined by the key type. The ARC4, ChaCha20, and XChaCha20 ciphers use this algorithm identifier.

ARC4

To use ARC4, use a key type of PSA_KEY_TYPE_ARC4 and algorithm id PSA_ALG_STREAM_CIPHER.

Warning

The ARC4 cipher is weak and deprecated and is only recommended for use in legacy applications.

The ARC4 cipher does not use an initialization vector (IV). When using a multi-part cipher operation with the PSA_ALG_STREAM_CIPHER algorithm and an ARC4 key, psa_cipher_generate_iv() and psa_cipher_set_iv() must not be called.

ChaCha20

To use ChaCha20, use a key type of PSA_KEY_TYPE_CHACHA20 and algorithm id PSA_ALG_STREAM_CIPHER.

Implementations must support the variant that is defined in ChaCha20 and Poly1305 for IETF Protocols [RFC8439] §2.4, which has a 96-bit nonce and a 32-bit counter. Implementations can optionally also support the original variant, as defined in ChaCha, a variant of Salsa20 [CHACHA20], which has a 64-bit nonce and a 64-bit counter. Except where noted, the [RFC8439] variant must be used.

ChaCha20 defines a nonce and an initial counter to be provided to the encryption and decryption operations. When using a ChaCha20 key with the PSA_ALG_STREAM_CIPHER algorithm, these values are provided using the initialization vector (IV) functions in the following ways:

  • A call to psa_cipher_encrypt() will generate a random 12-byte nonce, and set the counter value to zero. The random nonce is output as a 12-byte IV value in the output.

  • A call to psa_cipher_decrypt() will use first 12 bytes of the input buffer as the nonce and set the counter value to zero.

  • A call to psa_cipher_generate_iv() on a multi-part cipher operation will generate and return a random 12-byte nonce and set the counter value to zero.

  • A call to psa_cipher_set_iv() on a multi-part cipher operation can support the following IV sizes:

    • 12 bytes: the provided IV is used as the nonce, and the counter value is set to zero.

    • 16 bytes: the first four bytes of the IV are used as the counter value (encoded as little-endian), and the remaining 12 bytes are used as the nonce.

    • 8 bytes: the cipher operation uses the original [CHACHA20] definition of ChaCha20: the provided IV is used as the 64-bit nonce, and the 64-bit counter value is set to zero.

    • It is recommended that implementations do not support other sizes of IV.

XChaCha20

To use XChaCha20, use a key type of PSA_KEY_TYPE_XCHACHA20 and algorithm id PSA_ALG_STREAM_CIPHER.

XChaCha20 is a variation of ChaCha20 that uses a 192-bit nonce and a 64-bit counter. The larger nonce provides much lower probability of nonce misuse.

When using an XChaCha20 key with the PSA_ALG_STREAM_CIPHER algorithm, the nonce and an initial counter values are provided using the initialization vector (IV) functions in the following ways:

  • A call to psa_cipher_encrypt() will generate a random 24-byte nonce, and set the counter value to zero. The random nonce is output as a 24-byte IV value in the output.

  • A call to psa_cipher_decrypt() will use first 24 bytes of the input buffer as the nonce and set the counter value to zero.

  • A call to psa_cipher_generate_iv() on a multi-part cipher operation will generate and return a random 24-byte nonce and set the counter value to zero.

  • A call to psa_cipher_set_iv() on a multi-part cipher operation can support the following IV sizes:

    • 24 bytes: the provided IV is used as the nonce, and the counter value is set to zero.

    • 32 bytes: the first 8 bytes of the IV are used as the counter value (encoded as little-endian), and the remaining 24 bytes are used as the nonce.

    Other sizes of IV are invalid.

XChaCha20 is defined in XChaCha: eXtended-nonce ChaCha and AEAD_XChaCha20_Poly1305 [XCHACHA].

Compatible key types

PSA_KEY_TYPE_ARC4
PSA_KEY_TYPE_CHACHA20
PSA_KEY_TYPE_XCHACHA20

PSA_ALG_CTR (macro)

A stream cipher built using the Counter (CTR) mode of a block cipher.

#define PSA_ALG_CTR ((psa_algorithm_t)0x04c01000)

CTR is a stream cipher which is built from a block cipher. The underlying block cipher is determined by the key type. For example, to use AES-128-CTR, use this algorithm with a key of type PSA_KEY_TYPE_AES and a size of 128 bits (16 bytes).

The CTR block cipher mode is defined in NIST Special Publication 800-38A: Recommendation for Block Cipher Modes of Operation: Methods and Techniques [SP800-38A].

CTR mode operates using a counter block which is the same size as the cipher block length. The counter block is updated for each block, or a partial final block, that is encrypted or decrypted.

For the PSA_ALG_CTR algorithm, the counter block is initialized from the IV. The counter block is then treated as a single, big-endian encoded integer, and the counter block is updated by incrementing this integer by 1.

The security of CTR mode depends on using counter block values that are unique across all messages encrypted using the same key value. This is achieved by using suitable initial counter block values, the appropriate way to do this depends on the application use case:

  • If the application is using CTR mode to implement a protocol that specifies the construction of the IV, then the application must use a multi-part cipher operation, and call psa_cipher_set_iv() with the appropriate IV for encryption and decryption operations.

    Note

    The protocol must use the same counter block update strategy as the one specified here.

  • If the application is able to construct a unique nonce value for each time the same key is used to encrypt data, then it is recommended that the application uses a multi-part cipher operation, and call psa_cipher_set_iv() using the nonce as the IV for encryption and decryption operations.

    The nonce length, \(n\) bytes, must satisfy \(1\le n\le b\), where \(b\) is the cipher block size in bytes. To avoid a counter-block collision with other nonce values, the application must ensure that at most \(2^{8(b-n)}\) blocks of data are encrypted in any single operation.

    For example, when using CTR encryption with an AES key, the cipher block size is 16 bytes. The application can provide a 12-byte nonce when setting the IV. This leaves 4 bytes for the counter, allowing up to \(2^{32}\) blocks (64GB) of message data to be encrypted in each message.

  • Otherwise, it is recommended that the application uses a random IV value when encrypting data, and transmits the IV along with the ciphertext for use when decrypting the data. This can be achieved with either the single-part cipher functions or the multi-part cipher operation:

When using PSA_ALG_CTR, if the IV passed to psa_cipher_set_iv() is shorter than a cipher block, the initial counter block is formed by padding the end of the IV with zero bytes up to the block length.

Note

The cipher block length can be determined using PSA_BLOCK_CIPHER_BLOCK_LENGTH().

Compatible key types

PSA_KEY_TYPE_AES
PSA_KEY_TYPE_ARIA
PSA_KEY_TYPE_DES
PSA_KEY_TYPE_CAMELLIA
PSA_KEY_TYPE_SM4

PSA_ALG_CCM_STAR_NO_TAG (macro)

The CCM* cipher mode without authentication.

#define PSA_ALG_CCM_STAR_NO_TAG ((psa_algorithm_t)0x04c01300)

This is CCM* as specified in IEEE Standard for Low-Rate Wireless Networks [IEEE-CCM] §7, with a tag length of 0. For CCM* with a nonzero tag length, use the AEAD algorithm PSA_ALG_CCM.

The underlying block cipher is determined by the key type.

The IV generated or set in the cipher API is used as the nonce in the CCM* operation. An implementation must support the default IV length of 13. Support for setting a shorter IV is optional.

The maximum message length that can be encrypted is dependent on the length of the IV. See PSA_ALG_CCM for details of this relationship.

Usage in Zigbee

The Zigbee message encryption algorithm is based on CCM*. This is detailed in zigbee Specification [ZIGBEE] §B.1.1 and §A.

  • For unauthenticated messages — when tag length \(M = 0\) — the PSA_ALG_CCM_STAR_NO_TAG algorithm is used with an AES-128 key in a multi-part cipher operation. The 13-byte IV must be constructed as specified in [ZIGBEE], and provided to the operation using psa_cipher_set_iv().

    Note

    An implementation of Zigbee cannot use the single-part psa_cipher_encrypt() function, as this generates a random IV, which is not valid for the Zigbee protocol.

  • For authenticated messages — when tag length \(M \in \{4, 8, 16\}\) — the PSA_ALG_AEAD_WITH_SHORTENED_TAG(PSA_ALG_CCM, tag_length) algorithm is used with an AES-128 key, where tag_length is the required value of \(M\). The 13-byte nonce must be constructed as specified in [ZIGBEE].

    As the default tag length for CCM is 16, then PSA_ALG_CCM algorithm can be used when \(M = 16\).

  • To enable a single AES-128 key to be used for both the PSA_ALG_CCM_STAR_NO_TAG cipher and PSA_ALG_CCM AEAD algorithm, the key can be defined with the wildcard PSA_ALG_CCM_STAR_ANY_TAG permitted algorithm.

Compatible key types

PSA_KEY_TYPE_AES
PSA_KEY_TYPE_ARIA
PSA_KEY_TYPE_CAMELLIA
PSA_KEY_TYPE_SM4

PSA_ALG_CFB (macro)

A stream cipher built using the Cipher Feedback (CFB) mode of a block cipher.

#define PSA_ALG_CFB ((psa_algorithm_t)0x04c01100)

The underlying block cipher is determined by the key type. This is the variant of CFB where each iteration encrypts or decrypts a segment of the input that is the same length as the cipher block size. For example, using PSA_ALG_CFB with a key of type PSA_KEY_TYPE_AES will result in the AES-CFB-128 cipher.

CFB mode requires an initialization vector (IV) that is the same size as the cipher block length.

Note

The cipher block length can be determined using PSA_BLOCK_CIPHER_BLOCK_LENGTH().

The CFB block cipher mode is defined in NIST Special Publication 800-38A: Recommendation for Block Cipher Modes of Operation: Methods and Techniques [SP800-38A], using a segment size \(s\) equal to the block size \(b\). The definition in [SP800-38A] is extended to allow an incomplete final block of input, in which case the algorithm discards the final bytes of the key stream when encrypting or decrypting the final partial block.

Compatible key types

PSA_KEY_TYPE_AES
PSA_KEY_TYPE_ARIA
PSA_KEY_TYPE_DES
PSA_KEY_TYPE_CAMELLIA
PSA_KEY_TYPE_SM4

PSA_ALG_OFB (macro)

A stream cipher built using the Output Feedback (OFB) mode of a block cipher.

#define PSA_ALG_OFB ((psa_algorithm_t)0x04c01200)

The underlying block cipher is determined by the key type.

OFB mode requires an initialization vector (IV) that is the same size as the cipher block length. OFB mode requires that the IV is a nonce, and must be unique for each use of the mode with the same key.

Note

The cipher block length can be determined using PSA_BLOCK_CIPHER_BLOCK_LENGTH().

The OFB block cipher mode is defined in NIST Special Publication 800-38A: Recommendation for Block Cipher Modes of Operation: Methods and Techniques [SP800-38A].

Compatible key types

PSA_KEY_TYPE_AES
PSA_KEY_TYPE_ARIA
PSA_KEY_TYPE_DES
PSA_KEY_TYPE_CAMELLIA
PSA_KEY_TYPE_SM4

PSA_ALG_XTS (macro)

The XEX with Ciphertext Stealing (XTS) cipher mode of a block cipher.

#define PSA_ALG_XTS ((psa_algorithm_t)0x0440ff00)

XTS is a cipher mode which is built from a block cipher, designed for use in disk encryption. It requires at least one full cipher block length of input, but beyond this minimum the input does not need to be a whole number of blocks.

XTS mode uses two keys for the underlying block cipher. These are provided by using a key that is twice the normal key size for the cipher. For example, to use AES-256-XTS the application must create a key with type PSA_KEY_TYPE_AES and bit size 512.

XTS mode requires an initialization vector (IV) that is the same size as the cipher block length. The IV for XTS is typically defined to be the sector number of the disk block being encrypted or decrypted.

The XTS block cipher mode is defined in 1619-2018 --- IEEE Standard for Cryptographic Protection of Data on Block-Oriented Storage Devices [IEEE-XTS].

Compatible key types

PSA_KEY_TYPE_AES
PSA_KEY_TYPE_ARIA
PSA_KEY_TYPE_DES
PSA_KEY_TYPE_CAMELLIA
PSA_KEY_TYPE_SM4

PSA_ALG_ECB_NO_PADDING (macro)

The Electronic Codebook (ECB) mode of a block cipher, with no padding.

#define PSA_ALG_ECB_NO_PADDING ((psa_algorithm_t)0x04404400)

Warning

ECB mode does not protect the confidentiality of the encrypted data except in extremely narrow circumstances. It is recommended that applications only use ECB if they need to construct an operating mode that the implementation does not provide. Implementations are encouraged to provide the modes that applications need in preference to supporting direct access to ECB.

The underlying block cipher is determined by the key type.

This symmetric cipher mode can only be used with messages whose lengths are a multiple of the block size of the chosen block cipher.

ECB mode does not accept an initialization vector (IV). When using a multi-part cipher operation with this algorithm, psa_cipher_generate_iv() and psa_cipher_set_iv() must not be called.

Note

The cipher block length can be determined using PSA_BLOCK_CIPHER_BLOCK_LENGTH().

The ECB block cipher mode is defined in NIST Special Publication 800-38A: Recommendation for Block Cipher Modes of Operation: Methods and Techniques [SP800-38A].

Compatible key types

PSA_KEY_TYPE_AES
PSA_KEY_TYPE_ARIA
PSA_KEY_TYPE_DES
PSA_KEY_TYPE_CAMELLIA
PSA_KEY_TYPE_SM4

PSA_ALG_CBC_NO_PADDING (macro)

The Cipher Block Chaining (CBC) mode of a block cipher, with no padding.

#define PSA_ALG_CBC_NO_PADDING ((psa_algorithm_t)0x04404000)

The underlying block cipher is determined by the key type.

This symmetric cipher mode can only be used with messages whose lengths are a multiple of the block size of the chosen block cipher.

CBC mode requires an initialization vector (IV) that is the same size as the cipher block length.

Note

The cipher block length can be determined using PSA_BLOCK_CIPHER_BLOCK_LENGTH().

The CBC block cipher mode is defined in NIST Special Publication 800-38A: Recommendation for Block Cipher Modes of Operation: Methods and Techniques [SP800-38A].

Compatible key types

PSA_KEY_TYPE_AES
PSA_KEY_TYPE_ARIA
PSA_KEY_TYPE_DES
PSA_KEY_TYPE_CAMELLIA
PSA_KEY_TYPE_SM4

PSA_ALG_CBC_PKCS7 (macro)

The Cipher Block Chaining (CBC) mode of a block cipher, with PKCS#7 padding.

#define PSA_ALG_CBC_PKCS7 ((psa_algorithm_t)0x04404100)

The underlying block cipher is determined by the key type.

CBC mode requires an initialization vector (IV) that is the same size as the cipher block length.

Note

The cipher block length can be determined using PSA_BLOCK_CIPHER_BLOCK_LENGTH().

The CBC block cipher mode is defined in NIST Special Publication 800-38A: Recommendation for Block Cipher Modes of Operation: Methods and Techniques [SP800-38A]. The padding operation is defined by PKCS #7: Cryptographic Message Syntax Version 1.5 [RFC2315] §10.3.

Compatible key types

PSA_KEY_TYPE_AES
PSA_KEY_TYPE_ARIA
PSA_KEY_TYPE_DES
PSA_KEY_TYPE_CAMELLIA
PSA_KEY_TYPE_SM4

10.4.2. Single-part cipher functions

psa_cipher_encrypt (function)

Encrypt a message using a symmetric cipher.

psa_status_t psa_cipher_encrypt(psa_key_id_t key,
                                psa_algorithm_t alg,
                                const uint8_t * input,
                                size_t input_length,
                                uint8_t * output,
                                size_t output_size,
                                size_t * output_length);

Parameters

key

Identifier of the key to use for the operation. It must permit the usage PSA_KEY_USAGE_ENCRYPT.

alg

The cipher algorithm to compute: a value of type psa_algorithm_t such that PSA_ALG_IS_CIPHER(alg) is true.

input

Buffer containing the message to encrypt.

input_length

Size of the input buffer in bytes.

output

Buffer where the output is to be written. The output contains the IV followed by the ciphertext proper.

output_size

Size of the output buffer in bytes. This must be appropriate for the selected algorithm and key:

output_length

On success, the number of bytes that make up the output.

Returns: psa_status_t

PSA_SUCCESS

Success. The first (*output_length) bytes of output contain the encrypted output.

PSA_ERROR_BAD_STATE

The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_INVALID_HANDLE

key is not a valid key identifier.

PSA_ERROR_NOT_PERMITTED

The key does not have the PSA_KEY_USAGE_ENCRYPT flag, or it does not permit the requested algorithm.

PSA_ERROR_BUFFER_TOO_SMALL

The size of the output buffer is too small. PSA_CIPHER_ENCRYPT_OUTPUT_SIZE() or PSA_CIPHER_ENCRYPT_OUTPUT_MAX_SIZE() can be used to determine a sufficient buffer size.

PSA_ERROR_INVALID_ARGUMENT

The following conditions can result in this error:

  • alg is not a cipher algorithm.

  • key is not compatible with alg.

  • The input_length is not valid for the algorithm and key type. For example, the algorithm is a based on block cipher and requires a whole number of blocks, but the total input size is not a multiple of the block size.

PSA_ERROR_NOT_SUPPORTED

The following conditions can result in this error:

  • alg is not supported or is not a cipher algorithm.

  • key is not supported for use with alg.

  • input_length is too large for the implementation.

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

This function encrypts a message with a random initialization vector (IV). The length of the IV is PSA_CIPHER_IV_LENGTH(key_type, alg) where key_type is the type of key. The output of psa_cipher_encrypt() is the IV followed by the ciphertext.

Use the multi-part operation interface with a psa_cipher_operation_t object to provide other forms of IV or to manage the IV and ciphertext independently.

psa_cipher_decrypt (function)

Decrypt a message using a symmetric cipher.

psa_status_t psa_cipher_decrypt(psa_key_id_t key,
                                psa_algorithm_t alg,
                                const uint8_t * input,
                                size_t input_length,
                                uint8_t * output,
                                size_t output_size,
                                size_t * output_length);

Parameters

key

Identifier of the key to use for the operation. It must remain valid until the operation terminates. It must permit the usage PSA_KEY_USAGE_DECRYPT.

alg

The cipher algorithm to compute: a value of type psa_algorithm_t such that PSA_ALG_IS_CIPHER(alg) is true.

input

Buffer containing the message to decrypt. This consists of the IV followed by the ciphertext proper.

input_length

Size of the input buffer in bytes.

output

Buffer where the plaintext is to be written.

output_size

Size of the output buffer in bytes. This must be appropriate for the selected algorithm and key:

output_length

On success, the number of bytes that make up the output.

Returns: psa_status_t

PSA_SUCCESS

Success. The first (*output_length) bytes of output contain the plaintext.

PSA_ERROR_BAD_STATE

The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_INVALID_HANDLE

key is not a valid key identifier.

PSA_ERROR_NOT_PERMITTED

The key does not have the PSA_KEY_USAGE_DECRYPT flag, or it does not permit the requested algorithm.

PSA_ERROR_BUFFER_TOO_SMALL

The size of the output buffer is too small. PSA_CIPHER_DECRYPT_OUTPUT_SIZE() or PSA_CIPHER_DECRYPT_OUTPUT_MAX_SIZE() can be used to determine a sufficient buffer size.

PSA_ERROR_INVALID_PADDING

The algorithm uses padding, and the input does not contain valid padding.

PSA_ERROR_INVALID_ARGUMENT

The following conditions can result in this error:

  • alg is not a cipher algorithm.

  • key is not compatible with alg.

  • The input_length is not valid for the algorithm and key type. For example, the algorithm is a based on block cipher and requires a whole number of blocks, but the total input size is not a multiple of the block size.

PSA_ERROR_NOT_SUPPORTED

The following conditions can result in this error:

  • alg is not supported or is not a cipher algorithm.

  • key is not supported for use with alg.

  • input_length is too large for the implementation.

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

This function decrypts a message encrypted with a symmetric cipher.

The input to this function must contain the IV followed by the ciphertext, as output by psa_cipher_encrypt(). The IV must be PSA_CIPHER_IV_LENGTH(key_type, alg) bytes in length, where key_type is the type of key.

Use the multi-part operation interface with a psa_cipher_operation_t object to decrypt data which is not in the expected input format.

10.4.3. Multi-part cipher operations

psa_cipher_operation_t (typedef)

The type of the state object for multi-part cipher operations.

typedef /* implementation-defined type */ psa_cipher_operation_t;

Before calling any function on a cipher operation object, the application must initialize it by any of the following means:

This is an implementation-defined type. Applications that make assumptions about the content of this object will result in implementation-specific behavior, and are non-portable.

PSA_CIPHER_OPERATION_INIT (macro)

This macro returns a suitable initializer for a cipher operation object of type psa_cipher_operation_t.

#define PSA_CIPHER_OPERATION_INIT /* implementation-defined value */

psa_cipher_operation_init (function)

Return an initial value for a cipher operation object.

psa_cipher_operation_t psa_cipher_operation_init(void);

Returns: psa_cipher_operation_t

psa_cipher_encrypt_setup (function)

Set the key for a multi-part symmetric encryption operation.

psa_status_t psa_cipher_encrypt_setup(psa_cipher_operation_t * operation,
                                      psa_key_id_t key,
                                      psa_algorithm_t alg);

Parameters

operation

The operation object to set up. It must have been initialized as per the documentation for psa_cipher_operation_t and not yet in use.

key

Identifier of the key to use for the operation. It must remain valid until the operation terminates. It must permit the usage PSA_KEY_USAGE_ENCRYPT.

alg

The cipher algorithm to compute: a value of type psa_algorithm_t such that PSA_ALG_IS_CIPHER(alg) is true.

Returns: psa_status_t

PSA_SUCCESS

Success. The operation is now active.

PSA_ERROR_BAD_STATE

The following conditions can result in this error:

  • The operation state is not valid: it must be inactive.

  • The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_INVALID_HANDLE

key is not a valid key identifier.

PSA_ERROR_NOT_PERMITTED

The key does not have the PSA_KEY_USAGE_ENCRYPT flag, or it does not permit the requested algorithm.

PSA_ERROR_INVALID_ARGUMENT

The following conditions can result in this error:

  • alg is not a cipher algorithm.

  • key is not compatible with alg.

PSA_ERROR_NOT_SUPPORTED

The following conditions can result in this error:

  • alg is not supported or is not a cipher algorithm.

  • key is not supported for use with alg.

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

The sequence of operations to encrypt a message with a symmetric cipher is as follows:

  1. Allocate a cipher operation object which will be passed to all the functions listed here.

  2. Initialize the operation object with one of the methods described in the documentation for psa_cipher_operation_t, e.g. PSA_CIPHER_OPERATION_INIT.

  3. Call psa_cipher_encrypt_setup() to specify the algorithm and key.

  4. Call either psa_cipher_generate_iv() or psa_cipher_set_iv() to generate or set the initialization vector (IV), if the algorithm requires one. It is recommended to use psa_cipher_generate_iv() unless the protocol being implemented requires a specific IV value.

  5. Call psa_cipher_update() zero, one or more times, passing a fragment of the message each time.

  6. Call psa_cipher_finish().

After a successful call to psa_cipher_encrypt_setup(), the operation is active, and the application must eventually terminate the operation. The following events terminate an operation:

If psa_cipher_encrypt_setup() returns an error, the operation object is unchanged. If a subsequent function call with an active operation returns an error, the operation enters an error state.

To abandon an active operation, or reset an operation in an error state, call psa_cipher_abort().

See Multi-part operations.

psa_cipher_decrypt_setup (function)

Set the key for a multi-part symmetric decryption operation.

psa_status_t psa_cipher_decrypt_setup(psa_cipher_operation_t * operation,
                                      psa_key_id_t key,
                                      psa_algorithm_t alg);

Parameters

operation

The operation object to set up. It must have been initialized as per the documentation for psa_cipher_operation_t and not yet in use.

key

Identifier of the key to use for the operation. It must remain valid until the operation terminates. It must permit the usage PSA_KEY_USAGE_DECRYPT.

alg

The cipher algorithm to compute: a value of type psa_algorithm_t such that PSA_ALG_IS_CIPHER(alg) is true.

Returns: psa_status_t

PSA_SUCCESS

Success. The operation is now active.

PSA_ERROR_BAD_STATE

The following conditions can result in this error:

  • The operation state is not valid: it must be inactive.

  • The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_INVALID_HANDLE

key is not a valid key identifier.

PSA_ERROR_NOT_PERMITTED

The key does not have the PSA_KEY_USAGE_DECRYPT flag, or it does not permit the requested algorithm.

PSA_ERROR_INVALID_ARGUMENT

The following conditions can result in this error:

  • alg is not a cipher algorithm.

  • key is not compatible with alg.

PSA_ERROR_NOT_SUPPORTED

The following conditions can result in this error:

  • alg is not supported or is not a cipher algorithm.

  • key is not supported for use with alg.

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

The sequence of operations to decrypt a message with a symmetric cipher is as follows:

  1. Allocate a cipher operation object which will be passed to all the functions listed here.

  2. Initialize the operation object with one of the methods described in the documentation for psa_cipher_operation_t, e.g. PSA_CIPHER_OPERATION_INIT.

  3. Call psa_cipher_decrypt_setup() to specify the algorithm and key.

  4. Call psa_cipher_set_iv() with the initialization vector (IV) for the decryption, if the algorithm requires one. This must match the IV used for the encryption.

  5. Call psa_cipher_update() zero, one or more times, passing a fragment of the message each time.

  6. Call psa_cipher_finish().

After a successful call to psa_cipher_decrypt_setup(), the operation is active, and the application must eventually terminate the operation. The following events terminate an operation:

If psa_cipher_decrypt_setup() returns an error, the operation object is unchanged. If a subsequent function call with an active operation returns an error, the operation enters an error state.

To abandon an active operation, or reset an operation in an error state, call psa_cipher_abort().

See Multi-part operations.

psa_cipher_generate_iv (function)

Generate an initialization vector (IV) for a symmetric encryption operation.

psa_status_t psa_cipher_generate_iv(psa_cipher_operation_t * operation,
                                    uint8_t * iv,
                                    size_t iv_size,
                                    size_t * iv_length);

Parameters

operation

Active cipher operation.

iv

Buffer where the generated IV is to be written.

iv_size

Size of the iv buffer in bytes. This must be at least PSA_CIPHER_IV_LENGTH(key_type, alg) where key_type and alg are type of key and the algorithm respectively that were used to set up the cipher operation.

iv_length

On success, the number of bytes of the generated IV.

Returns: psa_status_t

PSA_SUCCESS

Success. The first (*iv_length) bytes of iv contain the generated IV.

PSA_ERROR_BAD_STATE

The following conditions can result in this error:

  • The cipher algorithm does not use an IV.

  • The operation state is not valid: it must be active, with no IV set.

  • The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_BUFFER_TOO_SMALL

The size of the iv buffer is too small. PSA_CIPHER_IV_LENGTH() or PSA_CIPHER_IV_MAX_SIZE can be used to determine a sufficient buffer size.

PSA_ERROR_INSUFFICIENT_ENTROPY

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

This function generates a random IV, nonce or initial counter value for the encryption operation as appropriate for the chosen algorithm, key type and key size.

The generated IV is always the default length for the key and algorithm: PSA_CIPHER_IV_LENGTH(key_type, alg), where key_type is the type of key and alg is the algorithm that were used to set up the operation. To generate different lengths of IV, use psa_generate_random() and psa_cipher_set_iv().

If the cipher algorithm does not use an IV, calling this function returns a PSA_ERROR_BAD_STATE error. For these algorithms, PSA_CIPHER_IV_LENGTH(key_type, alg) will be zero.

The application must call psa_cipher_encrypt_setup() before calling this function.

If this function returns an error status, the operation enters an error state and must be aborted by calling psa_cipher_abort().

psa_cipher_set_iv (function)

Set the initialization vector (IV) for a symmetric encryption or decryption operation.

psa_status_t psa_cipher_set_iv(psa_cipher_operation_t * operation,
                               const uint8_t * iv,
                               size_t iv_length);

Parameters

operation

Active cipher operation.

iv

Buffer containing the IV to use.

iv_length

Size of the IV in bytes.

Returns: psa_status_t

PSA_SUCCESS

Success.

PSA_ERROR_BAD_STATE

The following conditions can result in this error:

  • The cipher algorithm does not use an IV.

  • The operation state is not valid: it must be an active cipher encrypt operation, with no IV set.

  • The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_INVALID_ARGUMENT

The following conditions can result in this error:

  • The chosen algorithm does not use an IV.

  • iv_length is not valid for the chosen algorithm.

PSA_ERROR_NOT_SUPPORTED

iv_length is not supported for use with the operation’s algorithm and key.

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

This function sets the IV, nonce or initial counter value for the encryption or decryption operation.

If the cipher algorithm does not use an IV, calling this function returns a PSA_ERROR_BAD_STATE error. For these algorithms, PSA_CIPHER_IV_LENGTH(key_type, alg) will be zero.

The application must call psa_cipher_encrypt_setup() or psa_cipher_decrypt_setup() before calling this function.

If this function returns an error status, the operation enters an error state and must be aborted by calling psa_cipher_abort().

Note

When encrypting, psa_cipher_generate_iv() is recommended instead of using this function, unless implementing a protocol that requires a non-random IV.

psa_cipher_update (function)

Encrypt or decrypt a message fragment in an active cipher operation.

psa_status_t psa_cipher_update(psa_cipher_operation_t * operation,
                               const uint8_t * input,
                               size_t input_length,
                               uint8_t * output,
                               size_t output_size,
                               size_t * output_length);

Parameters

operation

Active cipher operation.

input

Buffer containing the message fragment to encrypt or decrypt.

input_length

Size of the input buffer in bytes.

output

Buffer where the output is to be written.

output_size

Size of the output buffer in bytes. This must be appropriate for the selected algorithm and key:

output_length

On success, the number of bytes that make up the returned output.

Returns: psa_status_t

PSA_SUCCESS

Success. The first (*output_length) bytes of output contain the output data.

PSA_ERROR_BAD_STATE

The following conditions can result in this error:

  • The operation state is not valid: it must be active, with an IV set if required for the algorithm.

  • The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_BUFFER_TOO_SMALL

The size of the output buffer is too small. PSA_CIPHER_UPDATE_OUTPUT_SIZE() or PSA_CIPHER_UPDATE_OUTPUT_MAX_SIZE() can be used to determine a sufficient buffer size.

PSA_ERROR_INVALID_ARGUMENT

The total input size passed to this operation is too large for this particular algorithm.

PSA_ERROR_NOT_SUPPORTED

The total input size passed to this operation is too large for the implementation.

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

The following must occur before calling this function:

  1. Call either psa_cipher_encrypt_setup() or psa_cipher_decrypt_setup(). The choice of setup function determines whether this function encrypts or decrypts its input.

  2. If the algorithm requires an IV, call psa_cipher_generate_iv() or psa_cipher_set_iv(). psa_cipher_generate_iv() is recommended when encrypting.

If this function returns an error status, the operation enters an error state and must be aborted by calling psa_cipher_abort().

Note

This function does not require the input to be aligned to any particular block boundary. If the implementation can only process a whole block at a time, it must consume all the input provided, but it might delay the end of the corresponding output until a subsequent call to psa_cipher_update() provides sufficient input, or a subsequent call to psa_cipher_finish() indicates the end of the input. The amount of data that can be delayed in this way is bounded by the associated output size macro: PSA_CIPHER_UPDATE_OUTPUT_SIZE() or PSA_CIPHER_FINISH_OUTPUT_SIZE().

psa_cipher_finish (function)

Finish encrypting or decrypting a message in a cipher operation.

psa_status_t psa_cipher_finish(psa_cipher_operation_t * operation,
                               uint8_t * output,
                               size_t output_size,
                               size_t * output_length);

Parameters

operation

Active cipher operation.

output

Buffer where the last part of the output is to be written.

output_size

Size of the output buffer in bytes. This must be appropriate for the selected algorithm and key:

output_length

On success, the number of bytes that make up the returned output.

Returns: psa_status_t

PSA_SUCCESS

Success. The first (*output_length) bytes of output contain the final output.

PSA_ERROR_BAD_STATE

The following conditions can result in this error:

  • The operation state is not valid: it must be active, with an IV set if required for the algorithm.

  • The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_BUFFER_TOO_SMALL

The size of the output buffer is too small. PSA_CIPHER_FINISH_OUTPUT_SIZE() or PSA_CIPHER_FINISH_OUTPUT_MAX_SIZE can be used to determine a sufficient buffer size.

PSA_ERROR_INVALID_PADDING

This is a decryption operation for an algorithm that includes padding, and the ciphertext does not contain valid padding.

PSA_ERROR_INVALID_ARGUMENT

The total input size passed to this operation is not valid for this particular algorithm. For example, the algorithm is a based on block cipher and requires a whole number of blocks, but the total input size is not a multiple of the block size.

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

The application must call psa_cipher_encrypt_setup() or psa_cipher_decrypt_setup() before calling this function. The choice of setup function determines whether this function encrypts or decrypts its input.

This function finishes the encryption or decryption of the message formed by concatenating the inputs passed to preceding calls to psa_cipher_update().

When this function returns successfully, the operation becomes inactive. If this function returns an error status, the operation enters an error state and must be aborted by calling psa_cipher_abort().

psa_cipher_abort (function)

Abort a cipher operation.

psa_status_t psa_cipher_abort(psa_cipher_operation_t * operation);

Parameters

operation

Initialized cipher operation.

Returns: psa_status_t

PSA_SUCCESS

Success. The operation object can now be discarded or reused.

PSA_ERROR_BAD_STATE

The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

Description

Aborting an operation frees all associated resources except for the operation object itself. Once aborted, the operation object can be reused for another operation by calling psa_cipher_encrypt_setup() or psa_cipher_decrypt_setup() again.

This function can be called any time after the operation object has been initialized as described in psa_cipher_operation_t.

In particular, calling psa_cipher_abort() after the operation has been terminated by a call to psa_cipher_abort() or psa_cipher_finish() is safe and has no effect.

10.4.4. Support macros

PSA_ALG_IS_STREAM_CIPHER (macro)

Whether the specified algorithm is a stream cipher.

#define PSA_ALG_IS_STREAM_CIPHER(alg) /* specification-defined value */

Parameters

alg

An algorithm identifier: a value of type psa_algorithm_t.

Returns

1 if alg is a stream cipher algorithm, 0 otherwise. This macro can return either 0 or 1 if alg is not a supported algorithm identifier or if it is not a symmetric cipher algorithm.

Description

A stream cipher is a symmetric cipher that encrypts or decrypts messages by applying a bitwise-xor with a stream of bytes that is generated from a key.

PSA_ALG_CCM_STAR_ANY_TAG (macro)

A wildcard algorithm that permits the use of the key with CCM* as both an AEAD and an unauthenticated cipher algorithm.

#define PSA_ALG_CCM_STAR_ANY_TAG ((psa_algorithm_t)0x04c09300)

If a block-cipher key specifies PSA_ALG_CCM_STAR_ANY_TAG as its permitted algorithm, then the key can be used with the PSA_ALG_CCM_STAR_NO_TAG unauthenticated cipher, the PSA_ALG_CCM AEAD algorithm, and truncated PSA_ALG_CCM AEAD algorithms.

PSA_CIPHER_ENCRYPT_OUTPUT_SIZE (macro)

A sufficient output buffer size for psa_cipher_encrypt(), in bytes.

#define PSA_CIPHER_ENCRYPT_OUTPUT_SIZE(key_type, alg, input_length) \
    /* implementation-defined value */

Parameters

key_type

A symmetric key type that is compatible with algorithm alg.

alg

A cipher algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_CIPHER(alg) is true.

input_length

Size of the input in bytes.

Returns

A sufficient output size for the specified key type and algorithm. If the key type or cipher algorithm is not recognized, or the parameters are incompatible, return 0. An implementation can return either 0 or a correct size for a key type and cipher algorithm that it recognizes, but does not support.

Description

If the size of the output buffer is at least this large, it is guaranteed that psa_cipher_encrypt() will not fail due to an insufficient buffer size. Depending on the algorithm, the actual size of the output might be smaller.

See also PSA_CIPHER_ENCRYPT_OUTPUT_MAX_SIZE.

PSA_CIPHER_ENCRYPT_OUTPUT_MAX_SIZE (macro)

A sufficient output buffer size for psa_cipher_encrypt(), for any of the supported key types and cipher algorithms.

#define PSA_CIPHER_ENCRYPT_OUTPUT_MAX_SIZE(input_length) \
    /* implementation-defined value */

Parameters

input_length

Size of the input in bytes.

Description

If the size of the output buffer is at least this large, it is guaranteed that psa_cipher_encrypt() will not fail due to an insufficient buffer size.

See also PSA_CIPHER_ENCRYPT_OUTPUT_SIZE().

PSA_CIPHER_DECRYPT_OUTPUT_SIZE (macro)

A sufficient output buffer size for psa_cipher_decrypt(), in bytes.

#define PSA_CIPHER_DECRYPT_OUTPUT_SIZE(key_type, alg, input_length) \
    /* implementation-defined value */

Parameters

key_type

A symmetric key type that is compatible with algorithm alg.

alg

A cipher algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_CIPHER(alg) is true.

input_length

Size of the input in bytes.

Returns

A sufficient output size for the specified key type and algorithm. If the key type or cipher algorithm is not recognized, or the parameters are incompatible, return 0. An implementation can return either 0 or a correct size for a key type and cipher algorithm that it recognizes, but does not support.

Description

If the size of the output buffer is at least this large, it is guaranteed that psa_cipher_decrypt() will not fail due to an insufficient buffer size. Depending on the algorithm, the actual size of the output might be smaller.

See also PSA_CIPHER_DECRYPT_OUTPUT_MAX_SIZE.

PSA_CIPHER_DECRYPT_OUTPUT_MAX_SIZE (macro)

A sufficient output buffer size for psa_cipher_decrypt(), for any of the supported key types and cipher algorithms.

#define PSA_CIPHER_DECRYPT_OUTPUT_MAX_SIZE(input_length) \
    /* implementation-defined value */

Parameters

input_length

Size of the input in bytes.

Description

If the size of the output buffer is at least this large, it is guaranteed that psa_cipher_decrypt() will not fail due to an insufficient buffer size.

See also PSA_CIPHER_DECRYPT_OUTPUT_SIZE().

PSA_CIPHER_IV_LENGTH (macro)

The default IV size for a cipher algorithm, in bytes.

#define PSA_CIPHER_IV_LENGTH(key_type, alg) /* implementation-defined value */

Parameters

key_type

A symmetric key type that is compatible with algorithm alg.

alg

A cipher algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_CIPHER(alg) is true.

Returns

The default IV size for the specified key type and algorithm. If the algorithm does not use an IV, return 0. If the key type or cipher algorithm is not recognized, or the parameters are incompatible, return 0. An implementation can return either 0 or a correct size for a key type and cipher algorithm that it recognizes, but does not support.

Description

The IV that is generated as part of a call to psa_cipher_encrypt() is always the default IV length for the algorithm.

This macro can be used to allocate a buffer of sufficient size to store the IV output from psa_cipher_generate_iv() when using a multi-part cipher operation.

See also PSA_CIPHER_IV_MAX_SIZE.

PSA_CIPHER_IV_MAX_SIZE (macro)

A sufficient buffer size for storing the IV generated by psa_cipher_generate_iv(), for any of the supported key types and cipher algorithms.

#define PSA_CIPHER_IV_MAX_SIZE /* implementation-defined value */

If the size of the IV buffer is at least this large, it is guaranteed that psa_cipher_generate_iv() will not fail due to an insufficient buffer size.

See also PSA_CIPHER_IV_LENGTH().

PSA_CIPHER_UPDATE_OUTPUT_SIZE (macro)

A sufficient output buffer size for psa_cipher_update(), in bytes.

#define PSA_CIPHER_UPDATE_OUTPUT_SIZE(key_type, alg, input_length) \
    /* implementation-defined value */

Parameters

key_type

A symmetric key type that is compatible with algorithm alg.

alg

A cipher algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_CIPHER(alg) is true.

input_length

Size of the input in bytes.

Returns

A sufficient output size for the specified key type and algorithm. If the key type or cipher algorithm is not recognized, or the parameters are incompatible, return 0. An implementation can return either 0 or a correct size for a key type and cipher algorithm that it recognizes, but does not support.

Description

If the size of the output buffer is at least this large, it is guaranteed that psa_cipher_update() will not fail due to an insufficient buffer size. The actual size of the output might be smaller in any given call.

See also PSA_CIPHER_UPDATE_OUTPUT_MAX_SIZE.

PSA_CIPHER_UPDATE_OUTPUT_MAX_SIZE (macro)

A sufficient output buffer size for psa_cipher_update(), for any of the supported key types and cipher algorithms.

#define PSA_CIPHER_UPDATE_OUTPUT_MAX_SIZE(input_length) \
    /* implementation-defined value */

Parameters

input_length

Size of the input in bytes.

Description

If the size of the output buffer is at least this large, it is guaranteed that psa_cipher_update() will not fail due to an insufficient buffer size.

See also PSA_CIPHER_UPDATE_OUTPUT_SIZE().

PSA_CIPHER_FINISH_OUTPUT_SIZE (macro)

A sufficient output buffer size for psa_cipher_finish().

#define PSA_CIPHER_FINISH_OUTPUT_SIZE(key_type, alg) \
    /* implementation-defined value */

Parameters

key_type

A symmetric key type that is compatible with algorithm alg.

alg

A cipher algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_CIPHER(alg) is true.

Returns

A sufficient output size for the specified key type and algorithm. If the key type or cipher algorithm is not recognized, or the parameters are incompatible, return 0. An implementation can return either 0 or a correct size for a key type and cipher algorithm that it recognizes, but does not support.

Description

If the size of the output buffer is at least this large, it is guaranteed that psa_cipher_finish() will not fail due to an insufficient buffer size. The actual size of the output might be smaller in any given call.

See also PSA_CIPHER_FINISH_OUTPUT_MAX_SIZE.

PSA_CIPHER_FINISH_OUTPUT_MAX_SIZE (macro)

A sufficient output buffer size for psa_cipher_finish(), for any of the supported key types and cipher algorithms.

#define PSA_CIPHER_FINISH_OUTPUT_MAX_SIZE /* implementation-defined value */

If the size of the output buffer is at least this large, it is guaranteed that psa_cipher_finish() will not fail due to an insufficient buffer size.

See also PSA_CIPHER_FINISH_OUTPUT_SIZE().

PSA_BLOCK_CIPHER_BLOCK_LENGTH (macro)

The block size of a block cipher.

#define PSA_BLOCK_CIPHER_BLOCK_LENGTH(type) /* specification-defined value */

Parameters

type

A cipher key type: a value of type psa_key_type_t.

Returns

The block size for a block cipher, or 1 for a stream cipher. The return value is undefined if type is not a supported cipher key type.

Description

Note

It is possible to build stream cipher algorithms on top of a block cipher, for example CTR mode (PSA_ALG_CTR). This macro only takes the key type into account, so it cannot be used to determine the size of the data that psa_cipher_update() might buffer for future processing in general.

See also PSA_BLOCK_CIPHER_BLOCK_MAX_SIZE.

PSA_BLOCK_CIPHER_BLOCK_MAX_SIZE (macro)

The maximum block size of a block cipher supported by the implementation.

#define PSA_BLOCK_CIPHER_BLOCK_MAX_SIZE /* implementation-defined value */

See also PSA_BLOCK_CIPHER_BLOCK_LENGTH().