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Fixup: uecc_ecdsa_sign_wrap() in pk_wrap.c

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The previous code passed `2 * NUM_ECC_BYTES` as the size limit for
the ECDSA signature, which fails to account for space required by
ASN.1 headers.
This commit is contained in:
Hanno Becker 2019-08-20 15:37:17 +01:00
parent 9a62f2dbfb
commit 9c7a359cc4
1 changed files with 20 additions and 3 deletions
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23
library/pk_wrap.c
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@ -653,15 +653,32 @@ static int uecc_eckey_sign_wrap( void *ctx, mbedtls_md_type_t md_alg,
{
const mbedtls_uecc_keypair *keypair = (const mbedtls_uecc_keypair *) ctx;
const struct uECC_Curve_t * uecc_curve = uECC_secp256r1();
uECC_sign(keypair->private_key, hash, hash_len, sig, uecc_curve);
/*
* RFC-4492 page 20:
*
* Ecdsa-Sig-Value ::= SEQUENCE {
* r INTEGER,
* s INTEGER
* }
*
* Size is at most
* 1 (tag) + 1 (len) + 1 (initial 0) + NUM_ECC_BYTES for each of r and s,
* twice that + 1 (tag) + 2 (len) for the sequence
* (assuming NUM_ECC_BYTES is less than 126 for r and s,
* and less than 124 (total len <= 255) for the sequence)
*/
const size_t max_secp256r1_ecdsa_sig_len = 3 + 2 * ( 3 + NUM_ECC_BYTES );
uECC_sign( keypair->private_key, hash, hash_len, sig, uecc_curve );
*sig_len = 2 * NUM_ECC_BYTES;
/* uECC owns its rng function pointer */
(void) f_rng;
(void) p_rng;
(void) md_alg;
return( pk_ecdsa_sig_asn1_from_uecc( sig, sig_len, 2*NUM_ECC_BYTES ) );
return( pk_ecdsa_sig_asn1_from_uecc( sig, sig_len, max_secp256r1_ecdsa_sig_len ) );
}
static void *uecc_eckey_alloc_wrap( void )