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psa: Simplify EC public key format

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Remove front matter from our EC key format, to make it just the contents
of an ECPoint as defined by SEC1 section 2.3.3.

As a consequence of the simplification, remove the restriction on not
being able to use an ECDH key with ECDSA. There is no longer any OID
specified when importing a key, so we can't reject importing of an ECDH
key for the purpose of ECDSA based on the OID.
This commit is contained in:
Jaeden Amero 2019-01-10 11:42:27 +00:00 • committed by Jaeden Amero
parent 97271b37c8
commit ccdce90adb
5 changed files with 127 additions and 178 deletions
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36
include/psa/crypto.h
View file

@ -482,6 +482,14 @@ psa_status_t psa_export_key(psa_key_handle_t handle,
* modulus INTEGER, -- n
* publicExponent INTEGER } -- e
* ```
* - For elliptic curve public keys (key types for which
* #PSA_KEY_TYPE_IS_ECC_PUBLIC_KEY is true), the format is the uncompressed
* representation defined by SEC1 §2.3.3 as the content of an ECPoint:
* Let `m` be the bit size associated with the curve, i.e. the bit size of
* `q` for a curve over `F_q`. The representation consists of:
* - The byte 0x04;
* - `x_P` as a `ceiling(m/8)`-byte string, big-endian;
* - `y_P` as a `ceiling(m/8)`-byte string, big-endian.
*
* For other public key types, the format is the DER representation defined by
* RFC 5280 as `SubjectPublicKeyInfo`, with the `subjectPublicKey` format
@ -509,30 +517,6 @@ psa_status_t psa_export_key(psa_key_handle_t handle,
* g INTEGER }
* DSAPublicKey ::= INTEGER -- public key, Y
* ```
* - For elliptic curve public keys (key types for which
* #PSA_KEY_TYPE_IS_ECC_PUBLIC_KEY is true),
* the `subjectPublicKey` format is defined by RFC 3279 §2.3.5 as
* `ECPoint`, which contains the uncompressed
* representation defined by SEC1 §2.3.3.
* The OID is `id-ecPublicKey`,
* and the parameters must be given as a `namedCurve` OID as specified in
* RFC 5480 §2.1.1.1 or other applicable standards.
* ```
* ansi-X9-62 OBJECT IDENTIFIER ::=
* { iso(1) member-body(2) us(840) 10045 }
* id-public-key-type OBJECT IDENTIFIER ::= { ansi-X9.62 2 }
* id-ecPublicKey OBJECT IDENTIFIER ::= { id-publicKeyType 1 }
*
* ECPoint ::= ...
* -- first 8 bits: 0x04;
* -- then x_P as a `ceiling(m/8)`-byte string, big endian;
* -- then y_P as a `ceiling(m/8)`-byte string, big endian;
* -- where `m` is the bit size associated with the curve,
* -- i.e. the bit size of `q` for a curve over `F_q`.
*
* EcpkParameters ::= CHOICE { -- other choices are not allowed
* namedCurve OBJECT IDENTIFIER }
* ```
*
* \param handle Handle to the key to export.
* \param[out] data Buffer where the key data is to be written.
@ -2160,7 +2144,9 @@ psa_status_t psa_key_derivation(psa_crypto_generator_t *generator,
* in the same format that psa_import_key()
* accepts. The standard formats for public
* keys are documented in the documentation
* of psa_export_public_key().
* of psa_export_public_key(). For EC keys, it
* must also be of the same group as the private
* key.
* \param peer_key_length Size of \p peer_key in bytes.
* \param alg The key agreement algorithm to compute
* (\c PSA_ALG_XXX value such that

24
include/psa/crypto_sizes.h
View file

@ -493,26 +493,16 @@
/* Maximum size of the export encoding of an ECC public key.
*
* SubjectPublicKeyInfo ::= SEQUENCE {
* algorithm AlgorithmIdentifier,
* subjectPublicKey BIT STRING } -- contains ECPoint
* AlgorithmIdentifier ::= SEQUENCE {
* algorithm OBJECT IDENTIFIER,
* parameters OBJECT IDENTIFIER } -- namedCurve
* ECPoint ::= ...
* -- first 8 bits: 0x04;
* -- then x_P as a `ceiling(m/8)`-byte string, big endian;
* -- then y_P as a `ceiling(m/8)`-byte string, big endian;
* -- where `m` is the bit size associated with the curve.
* The representation of an ECC public key is:
* - The byte 0x04;
* - `x_P` as a `ceiling(m/8)`-byte string, big-endian;
* - `y_P` as a `ceiling(m/8)`-byte string, big-endian;
* - where m is the bit size associated with the curve.
*
* - 2 * 4 bytes of SEQUENCE overhead;
* - 1 + 1 + 7 bytes of algorithm (id-ecPublicKey OID);
* - 1 + 1 + 12 bytes of namedCurve OID;
* - 4 bytes of BIT STRING overhead;
* - 1 byte + 2 * point size in ECPoint.
* - 1 byte + 2 * point size.
*/
#define PSA_KEY_EXPORT_ECC_PUBLIC_KEY_MAX_SIZE(key_bits) \
(2 * PSA_BITS_TO_BYTES(key_bits) + 36)
(2 * PSA_BITS_TO_BYTES(key_bits) + 1)
/* Maximum size of the export encoding of an ECC key pair.
*