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Parse RSA parameters DP, DQ and QP from PKCS1 private keys

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Otherwise these values are recomputed in mbedtls_rsa_deduce_crt, which
currently suffers from side channel issues in the computation of QP (see
https://eprint.iacr.org/2020/055). By loading the pre-computed values not
only is the side channel avoided, but runtime overhead of loading RSA keys
is reduced.

Discussion in https://github.com/ARMmbed/mbed-crypto/issues/347
This commit is contained in:
Jack Lloyd 2020-01-22 17:34:29 -05:00
parent d27a88438f
commit 80cc811039
2 changed files with 27 additions and 8 deletions
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27
library/pkparse.c
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@ -769,16 +769,31 @@ static int pk_parse_key_pkcs1_der( mbedtls_rsa_context *rsa,
goto cleanup;
p += len;
/* Import DP */
if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
MBEDTLS_ASN1_INTEGER ) ) != 0 ||
( ret = mbedtls_mpi_read_binary( &rsa->DP, p, len ) ) != 0 )
goto cleanup;
p += len;
/* Import DQ */
if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
MBEDTLS_ASN1_INTEGER ) ) != 0 ||
( ret = mbedtls_mpi_read_binary( &rsa->DQ, p, len ) ) != 0 )
goto cleanup;
p += len;
/* Import QP */
if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
MBEDTLS_ASN1_INTEGER ) ) != 0 ||
( ret = mbedtls_mpi_read_binary( &rsa->QP, p, len ) ) != 0 )
goto cleanup;
p += len;
/* Complete the RSA private key */
if( ( ret = mbedtls_rsa_complete( rsa ) ) != 0 )
goto cleanup;
/* Check optional parameters */
if( ( ret = mbedtls_asn1_get_mpi( &p, end, &T ) ) != 0 ||
( ret = mbedtls_asn1_get_mpi( &p, end, &T ) ) != 0 ||
( ret = mbedtls_asn1_get_mpi( &p, end, &T ) ) != 0 )
goto cleanup;
if( p != end )
{
ret = MBEDTLS_ERR_PK_KEY_INVALID_FORMAT +