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Define algorithms for EdDSA

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Define algorithms for PureEdDSA and for HashEdDSA, the EdDSA variants
defined by RFC 8032.

The encoding for HashEdDSA needs to encode the hash algorithm so that
the hash can be calculated by passing PSA_ALG_SIGN_GET_HASH(sig_alg)
to psa_hash_compute() or psa_hash_setup(). As a consequence,
Ed25519ph (using SHA-512) and Ed448ph (using SHAKE256) need to have
different algorithm encodings (the key is enough to tell them apart,
but it is not known while hashing). Another consequence is that the
API needs to recognize the Ed448 prehash (64 bytes of SHAKE256 output)
as a hash algorithm.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-02-24 21:52:21 +01:00
parent 67546802fe
commit 3a1101a122
4 changed files with 109 additions and 12 deletions
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81
include/psa/crypto_values.h
View file

@ -571,7 +571,9 @@
/** The twisted Edwards curves Ed25519 and Ed448.
*
* These curves are suitable for EdDSA.
* These curves are suitable for EdDSA (#PSA_ALG_PURE_EDDSA for both curves,
* #PSA_ALG_ED25519PH for the 256-bit curve,
* #PSA_ALG_ED448PH for the 448-bit curve).
*
* This family comprises the following twisted Edwards curves:
* - 256-bit: Edwards25519, the twisted Edwards curve birationally equivalent
@ -801,6 +803,13 @@
#define PSA_ALG_SHA3_384 ((psa_algorithm_t)0x02000012)
/** SHA3-512 */
#define PSA_ALG_SHA3_512 ((psa_algorithm_t)0x02000013)
/** The first 64 bytes of the SHAKE256 output.
*
* This is the prehashing for Ed448ph (see #PSA_ALG_ED448PH). For other
* scenarios where a hash function based on SHA3/SHAKE is desired, SHA3-512
* has the same output size and a (theoretically) higher security strength.
*/
#define PSA_ALG_SHAKE256_64 ((psa_algorithm_t)0x02000014)
/** In a hash-and-sign algorithm policy, allow any hash algorithm.
*
@ -1358,6 +1367,74 @@
#define PSA_ALG_IS_RANDOMIZED_ECDSA(alg) \
(PSA_ALG_IS_ECDSA(alg) && !PSA_ALG_ECDSA_IS_DETERMINISTIC(alg))
/** Edwards-curve digital signature algorithm without prehashing (PureEdDSA),
* using standard parameters.
*
* Contexts are not supported in the current version of this specification
* because there is no suitable signature interface that can take the
* context as a parameter. A future version of this specification may add
* suitable functions and extend this algorithm to support contexts.
*
* PureEdDSA requires an elliptic curve key on a twisted Edwards curve.
* In this specification, the following curves are supported:
* - #PSA_ECC_FAMILY_TWISTED_EDWARDS, 255-bit: Ed25519 as specified
* in RFC 8032.
* The curve is Edwards25519.
* The hash function used internally is SHA-512.
* - #PSA_ECC_FAMILY_TWISTED_EDWARDS, 448-bit: Ed448 as specified
* in RFC 8032.
* The curve is Edwards448.
* The hash function used internally is the first 114 bytes of the
* SHAKE256 output, with
* `dom4(1, "") = ASCII("SigEd448") || 0x01 0x00`
* prepended to the input.
*
* This algorithm can be used with psa_sign_message() and
* psa_verify_message(). Since there is no prehashing, it cannot be used
* with psa_sign_hash() or psa_verify_hash().
*
* The signature format is the concatenation of R and S as defined by
* RFC 8032 §5.1.6 and §5.2.6 (a 64-byte string for Ed25519, a 114-byte
* string for Ed448).
*/
#define PSA_ALG_PURE_EDDSA ((psa_algorithm_t)0x06000800)
#define PSA_ALG_HASH_EDDSA_BASE ((psa_algorithm_t)0x06000900)
#define PSA_ALG_IS_HASH_EDDSA(alg) \
(((alg) & ~PSA_ALG_HASH_MASK) == PSA_ALG_HASH_EDDSA_BASE)
/** Edwards-curve digital signature algorithm with prehashing (HashEdDSA),
* using SHAKE256 and the Edwards448 curve.
*
* See #PSA_ALG_PURE_EDDSA regarding context support and the signature format.
*
* This algorithm is Ed25519 as specified in RFC 8032.
* The curve is Edwards25519.
* The input is first hashed with SHA-512.
* The hash function used internally is SHA-512, with
* `dom2(0, "") = ASCII("SigEd25519 no Ed25519 collisions") || 0x00 0x00`
* prepended to the input.
*/
#define PSA_ALG_ED25519PH \
(PSA_ALG_HASH_EDDSA_BASE | (PSA_ALG_SHA_512 & PSA_ALG_HASH_MASK))
/** Edwards-curve digital signature algorithm with prehashing (HashEdDSA),
* using SHAKE256 and the Edwards448 curve.
*
* See #PSA_ALG_PURE_EDDSA regarding context support and the signature format.
*
* This algorithm is Ed448 as specified in RFC 8032.
* The curve is Edwards448.
* The input is first hashed by taking the first 64 bytes of the SHAKE256
* output.
* The hash function used internally is the first 114 bytes of the
* SHAKE256 output, with
* `dom4(0, "") = ASCII("SigEd448") || 0x00 0x00`
* prepended to the input.
*/
#define PSA_ALG_ED448PH \
(PSA_ALG_HASH_EDDSA_BASE | (PSA_ALG_SHAKE256_64 & PSA_ALG_HASH_MASK))
/* Default definition, to be overridden if the library is extended with
* more hash-and-sign algorithms that we want to keep out of this header
* file. */
@ -1378,7 +1455,7 @@
*/
#define PSA_ALG_IS_HASH_AND_SIGN(alg) \
(PSA_ALG_IS_RSA_PSS(alg) || PSA_ALG_IS_RSA_PKCS1V15_SIGN(alg) || \
PSA_ALG_IS_ECDSA(alg) || \
PSA_ALG_IS_ECDSA(alg) || PSA_ALG_IS_HASH_EDDSA(alg) || \
PSA_ALG_IS_VENDOR_HASH_AND_SIGN(alg))
/** Get the hash used by a hash-and-sign signature algorithm.