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OpenSSL: Use BN_bn2binpad() or BN_bn2bin_padded() if available

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This converts crypto_bignum_to_bin() to use the OpenSSL/BoringSSL
functions BN_bn2binpad()/BN_bn2bin_padded(), when available, to avoid
differences in runtime and memory access patterns depending on the
leading bytes of the BIGNUM value.

OpenSSL 1.0.2 and LibreSSL do not include such functions, so those cases
are still using the previous implementation where the BN_num_bytes()
call may result in different memory access pattern.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
This commit is contained in:
Jouni Malinen 2019-04-25 19:23:05 +03:00 committed by Jouni Malinen
parent 7958223fdc
commit 1e237903f5
1 changed files with 16 additions and 0 deletions
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16
src/crypto/crypto_openssl.c
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@ -1295,7 +1295,13 @@ void crypto_bignum_deinit(struct crypto_bignum *n, int clear)
int crypto_bignum_to_bin(const struct crypto_bignum *a,
u8 *buf, size_t buflen, size_t padlen)
{
#ifdef OPENSSL_IS_BORINGSSL
#else /* OPENSSL_IS_BORINGSSL */
#if OPENSSL_VERSION_NUMBER >= 0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
#else
int num_bytes, offset;
#endif
#endif /* OPENSSL_IS_BORINGSSL */
if (TEST_FAIL())
return -1;
@ -1303,6 +1309,14 @@ int crypto_bignum_to_bin(const struct crypto_bignum *a,
if (padlen > buflen)
return -1;
#ifdef OPENSSL_IS_BORINGSSL
if (BN_bn2bin_padded(buf, padlen, (const BIGNUM *) a) == 0)
return -1;
return padlen;
#else /* OPENSSL_IS_BORINGSSL */
#if OPENSSL_VERSION_NUMBER >= 0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
return BN_bn2binpad((const BIGNUM *) a, buf, padlen);
#else
num_bytes = BN_num_bytes((const BIGNUM *) a);
if ((size_t) num_bytes > buflen)
return -1;
@ -1315,6 +1329,8 @@ int crypto_bignum_to_bin(const struct crypto_bignum *a,
BN_bn2bin((const BIGNUM *) a, buf + offset);
return num_bytes + offset;
#endif
#endif /* OPENSSL_IS_BORINGSSL */
}