About this document

Release information

The change history table lists the changes that have been made to this document.

Table 1 Document revision history





February 2022

Beta 0


Initial release of the 1.1 PAKE Extension specification

October 2022

Beta 1


Relicensed as open source under CC BY-SA 4.0.

The detailed changes in each release are described in Document change history.

PSA Certified Crypto API

Copyright © 2022 Arm Limited and/or its affiliates. The copyright statement reflects the fact that some draft issues of this document have been released, to a limited circulation.


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About the license

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  1. Changes are made related to the defined terms, to align those defined terms with the terminology in CC BY-SA 4.0 rather than Apache 2.0 (for example, changing “Work” to “Licensed Material”).

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Source code

Source code samples in this work are licensed under the Apache License, Version 2.0 (the “License”); you may not use such samples except in compliance with the License. You may obtain a copy of the License at apache.org/licenses/LICENSE-2.0.

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This document refers to the following documents.

Table 2 Documents referenced by this document


Document Number



IHI 0086

PSA Certified Crypto API. arm-software.github.io/psa-api/crypto


Arm Ltd, Mbed TLS. github.com/ARMmbed/mbedtls


Standards for Efficient Cryptography, SEC 1: Elliptic Curve Cryptography, May 2009. www.secg.org/sec1-v2.pdf


IETF, Schnorr Non-interactive Zero-Knowledge Proof, September 2017. tools.ietf.org/html/rfc8235.html


IETF, J-PAKE: Password-Authenticated Key Exchange by Juggling, September 2017. tools.ietf.org/html/rfc8236.html

Terms and abbreviations

This document uses the following terms and abbreviations.

Table 3 Terms and abbreviations



AEAD See Authenticated Encryption with Associated Data.

A finite sequence of steps to perform a particular operation.

In this specification, an algorithm is a cipher or a related function. Other texts call this a cryptographic mechanism.


Application Programming Interface.


See Public-key cryptography.

Authenticated Encryption with Associated Data (AEAD)

A type of encryption that provides confidentiality and authenticity of data using symmetric keys.


In this specification, a unit of storage comprising eight bits, also called an octet.


An algorithm used for encryption or decryption with a symmetric key.


The component that performs cryptographic operations. A cryptoprocessor might contain a keystore and countermeasures against a range of physical and timing attacks.


A cryptographic hash function, or the value returned by such a function.


A type of MAC that uses a cryptographic key with a hash function.

Implementation defined

Behavior that is not defined by the architecture, but is defined and documented by individual implementations.

Initialization vector (IV)

An additional input that is not part of the message. It is used to prevent an attacker from making any correlation between cipher text and plain text.

This specification uses the term for such initial inputs in all contexts. For example, the initial counter in CTR mode is called the IV.

IV See Initialization vector.
KDF See Key Derivation Function.
Key agreement

An algorithm for two or more parties to establish a common secret key.

Key Derivation Function (KDF)

Key Derivation Function. An algorithm for deriving keys from secret material.

Key identifier

A reference to a cryptographic key. Key identifiers in the Crypto API are 32-bit integers.

Key policy

Key metadata that describes and restricts what a key can be used for.

Key size

The size of a key as defined by common conventions for each key type. For keys that are built from several numbers of strings, this is the size of a particular one of these numbers or strings.

This specification expresses key sizes in bits.

Key type

Key metadata that describes the structure and content of a key.


A hardware or software component that protects, stores, and manages cryptographic keys.


Key metadata that describes when a key is destroyed.

MAC See Message Authentication Code.
Message Authentication Code (MAC)

A short piece of information used to authenticate a message. It is created and verified using a symmetric key.

Message digest

A hash of a message. Used to determine if a message has been tampered.

Multi-part operation

An API which splits a single cryptographic operation into a sequence of separate steps.

Non-extractable key

A key with a key policy that prevents it from being read by ordinary means.


Used as an input for certain AEAD algorithms. Nonces must not be reused with the same key because this can break a cryptographic protocol.

PAKE See Password-authenticated key exchange.
Password-authenticated key exchange (PAKE)

An interactive method for two or more parties to establish cryptographic keys based on knowledge of a low entropy secret, such as a password.

This can provide strong security for communication from a weak password, because the password is not directly communicated as part of the key exchange.

Persistent key

A key that is stored in protected non-volatile memory.


Platform Security Architecture

Public-key cryptography

A type of cryptographic system that uses key pairs. A keypair consists of a (secret) private key and a public key (not secret). A public key cryptographic algorithm can be used for key distribution and for digital signatures.


Used as an input for certain algorithms, such as key derivations.


The output of a digital signature scheme that uses an asymmetric keypair. Used to establish who produced a message.

Single-part function

An API that implements the cryptographic operation in a single function call.

Specification defined

Behavior that is defined by this specification.


A type of cryptographic algorithm that uses a single key. A symmetric key can be used with a block cipher or a stream cipher.

Volatile key

A key that has a short lifespan and is guaranteed not to exist after a restart of an application instance.


Typographical conventions

The typographical conventions are:


Introduces special terminology, and denotes citations.


Used for assembler syntax descriptions, pseudocode, and source code examples.

Also used in the main text for instruction mnemonics and for references to other items appearing in assembler syntax descriptions, pseudocode, and source code examples.

small capitals

Used for some common terms such as implementation defined.

Used for a few terms that have specific technical meanings, and are included in the Terms and abbreviations.

Red text

Indicates an open issue.

Blue text

Indicates a link. This can be

  • A cross-reference to another location within the document

  • A URL, for example example.com


Numbers are normally written in decimal. Binary numbers are preceded by 0b, and hexadecimal numbers by 0x.

In both cases, the prefix and the associated value are written in a monospace font, for example 0xFFFF0000. To improve readability, long numbers can be written with an underscore separator between every four characters, for example 0xFFFF_0000_0000_0000. Ignore any underscores when interpreting the value of a number.

Current status and anticipated changes

This document is at Beta quality status which has a particular meaning to Arm of which the recipient must be aware. A Beta quality specification will be sufficiently stable & committed for initial product development, however all aspects of the architecture described herein remain SUBJECT TO CHANGE. Please ensure that you have the latest revision.


We welcome feedback on the PSA Certified API documentation.

If you have comments on the content of this book, visit github.com/arm-software/psa-api/issues to create a new issue at the PSA Certified API GitHub project. Give:

  • The title (Crypto API).

  • The number and issue (AES 0058 1.1 PAKE Extension Beta (Issue 1)).

  • The location in the document to which your comments apply.

  • A concise explanation of your comments.

We also welcome general suggestions for additions and improvements.