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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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24
include/psa/crypto_sizes.h
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@ -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.
*