| Message ID | 20220421185740.799271-1-stefanb@linux.ibm.com |
|---|---|
| State | New |
| Headers | show |
| Series | ecdsa: Fix incorrect usage of vli_cmp | expand |
On 4/21/22 14:57, Stefan Berger wrote: > Fix incorrect usage of vli_cmp when calculating the value of res.x. For > signature verification to succeed, res.x must be the same as the r > component of the signature which is in the range of [1..n-1] with 'n' > being the order of the curve. Therefore, when res.x equals n calculate > res.x = res.x - n as well. Signature verification could have previously > unnecessarily failed in extremely rare cases. Actually, I am withdrawing this patch. Before this patch res.x could equal 'n' and then wouldn't match r due to the range of r being [1..n-1]. Now if res.x equals 'n' then res.x - n will be 0 and again will not match 'r' due to the range of r being [1..n-1]. So it makes no difference whether vli_cmp() == 1 or vli_cmp() >= 1 and the concern above about rare cases not verifying the signature is wrong. Stefan > > Fixes: 4e6602916bc6 ("crypto: ecdsa - Add support for ECDSA signature verification") > Cc: <stable@vger.kernel.org> > Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> > --- > crypto/ecdsa.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c > index b3a8a6b572ba..674ab9275366 100644 > --- a/crypto/ecdsa.c > +++ b/crypto/ecdsa.c > @@ -120,8 +120,8 @@ static int _ecdsa_verify(struct ecc_ctx *ctx, const u64 *hash, const u64 *r, con > /* res = u1*G + u2 * pub_key */ > ecc_point_mult_shamir(&res, u1, &curve->g, u2, &ctx->pub_key, curve); > > - /* res.x = res.x mod n (if res.x > order) */ > - if (unlikely(vli_cmp(res.x, curve->n, ndigits) == 1)) > + /* res.x = res.x mod n (if res.x >= order) */ > + if (unlikely(vli_cmp(res.x, curve->n, ndigits) >= 0)) > /* faster alternative for NIST p384, p256 & p192 */ > vli_sub(res.x, res.x, curve->n, ndigits); >
diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c index b3a8a6b572ba..674ab9275366 100644 --- a/crypto/ecdsa.c +++ b/crypto/ecdsa.c @@ -120,8 +120,8 @@ static int _ecdsa_verify(struct ecc_ctx *ctx, const u64 *hash, const u64 *r, con /* res = u1*G + u2 * pub_key */ ecc_point_mult_shamir(&res, u1, &curve->g, u2, &ctx->pub_key, curve); - /* res.x = res.x mod n (if res.x > order) */ - if (unlikely(vli_cmp(res.x, curve->n, ndigits) == 1)) + /* res.x = res.x mod n (if res.x >= order) */ + if (unlikely(vli_cmp(res.x, curve->n, ndigits) >= 0)) /* faster alternative for NIST p384, p256 & p192 */ vli_sub(res.x, res.x, curve->n, ndigits);
Fix incorrect usage of vli_cmp when calculating the value of res.x. For signature verification to succeed, res.x must be the same as the r component of the signature which is in the range of [1..n-1] with 'n' being the order of the curve. Therefore, when res.x equals n calculate res.x = res.x - n as well. Signature verification could have previously unnecessarily failed in extremely rare cases. Fixes: 4e6602916bc6 ("crypto: ecdsa - Add support for ECDSA signature verification") Cc: <stable@vger.kernel.org> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> --- crypto/ecdsa.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)