asymmetric keys: explicitly add the leading zero byte to encoded message
Subsystems (2)
PATCH 1/1 asymmetric keys: explicitly add the leading zero byte to encoded message
From: Chun-Yi Lee <[email protected]>
Per PKCS1 spec, the EMSA-PKCS1-v1_5 encoded message is leading by 0x00 0x01 in its first 2 bytes. The leading zero byte is suppressed by MPI so we pass a pointer to the _preceding_ byte to RSA_verify() in original code, but it has risk for the byte is not zero because it's not in EM buffer's scope, neither RSA_verify() nor mpi_get_buffer() didn't take care the leading byte.
To avoid the risk, that's better we explicitly add the leading zero byte to EM for pass to RSA_verify(). This patch allocate a _EM buffer to capture the result from RSA_I2OSP(), then set the first byte to zero in EM and copy the remaining bytes from _EM.
Cc Rusty Russell <[email protected]>
Cc Josh Boyer <[email protected]>
Cc Randy Dunlap <[email protected]>
Cc Herbert Xu <[email protected]>
Cc "David S. Miller" <[email protected]>
Cc David Howells <[email protected]>
Signed-off-by Chun-Yi Lee <[email protected]>
--- crypto/asymmetric_keys/rsa.c | 14 ++++++++++---- 1 files changed, 10 insertions(+), 4 deletions(-)
crypto/asymmetric_keys/rsa.c +10 -4
@@ -303,6 +303,7 @@ static int RSA_verify_signature(const struct public_key *key,/* Variables as per RFC3447 sec 8.2.2 */ const u8 *H = sig->digest;u8 *EM =NULL ; +u8 *_EM =NULL ;MPI m =NULL ;size_t k;
@@ -337,14 +338,19 @@ static int RSA_verify_signature(const struct public_key *key,/* (2c) Convert the message representative (m) to an encoded message * (EM) of length k octets. * -* NOTE! The leading zero byte is suppressed by MPI, so we pass a -* pointer to the _preceding_ byte to RSA_verify()! +* NOTE! The leading zero byte is suppressed by MPI, so we add it +* back to EM before input to RSA_verify()! */ - ret =RSA_I2OSP (m, k, &EM ); + ret =RSA_I2OSP (m, k, &_EM);if (ret <0 ) goto error; - ret =RSA_verify (H ,EM -1 , k, sig->digest_size, +EM =kmalloc (k,GFP_KERNEL ); +memset (EM ,0 ,1 ); +memcpy (EM +1 , _EM, k-1 ); +kfree (_EM); + + ret =RSA_verify (H ,EM , k, sig->digest_size, RSA_ASN1_templates[sig->pkey_hash_algo].data, RSA_ASN1_templates[sig->pkey_hash_algo].size);
Signature · 1 line
1.6.4.2