| Message ID | 20240312183618.1211745-5-stefanb@linux.vnet.ibm.com |
|---|---|
| State | New |
| Headers | show |
| Series | Add support for NIST P521 to ecdsa | expand |
On Tue Mar 12, 2024 at 8:36 PM EET, Stefan Berger wrote: > From: Stefan Berger <stefanb@linux.ibm.com> > > res.x has been calculated by ecc_point_mult_shamir, which uses > 'mod curve_prime'. The curve_prime 'p' is typically larger than the > curve_order 'n' and therefore it is possible that p > res.x >= n. The first sentence is an incomplete sentence. A lot of cross-referencing from e.g. elixir is required to "decipher" this commit message :-) I do get that math here is complicated but for that matter each commit message should be written with care, minimizing the require cross- referencing. These commit messages are adding extra layer of salt. > > If res.x >= n then res.x mod n can be calculated by iteratively sub- > tracting n from res.x until n > res.x. For NIST P192/256/384 this can be > done in a single subtraction. This can also be done in a single > subtraction for NIST P521. > > The mathematical reason why a single subtraction is sufficient is > due to the values of 'p' and 'n' of the NIST curves where the following > holds true: > > note: max(res.x) = p - 1 > > max(res.x) - n < n > p - 1 - n < n > p - 1 < 2n => true for the NIST curves > > Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> > Tested-by: Lukas Wunner <lukas@wunner.de> What was there to test in this anyway? I see only comment change below. > --- > crypto/ecdsa.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c > index 64e1e69d53ba..1814f009f971 100644 > --- a/crypto/ecdsa.c > +++ b/crypto/ecdsa.c > @@ -122,7 +122,7 @@ static int _ecdsa_verify(struct ecc_ctx *ctx, const u64 *hash, const u64 *r, con > > /* res.x = res.x mod n (if res.x > order) */ > if (unlikely(vli_cmp(res.x, curve->n, ndigits) == 1)) > - /* faster alternative for NIST p384, p256 & p192 */ > + /* faster alternative for NIST p521, p384, p256 & p192 */ > vli_sub(res.x, res.x, curve->n, ndigits); > > if (!vli_cmp(res.x, r, ndigits)) BR, Jarkko
On Mon, Mar 18, 2024 at 10:33:47PM +0200, Jarkko Sakkinen wrote: > On Tue Mar 12, 2024 at 8:36 PM EET, Stefan Berger wrote: > > Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> > > Tested-by: Lukas Wunner <lukas@wunner.de> > > What was there to test in this anyway? I see only comment change below. The full series was tested, irrespective of the content of the individual patches. Thanks, Lukas
On Mon Mar 18, 2024 at 10:39 PM EET, Lukas Wunner wrote: > On Mon, Mar 18, 2024 at 10:33:47PM +0200, Jarkko Sakkinen wrote: > > On Tue Mar 12, 2024 at 8:36 PM EET, Stefan Berger wrote: > > > Signed-off-by: Stefan Berger <stefanb@linux.ibm.com> > > > Tested-by: Lukas Wunner <lukas@wunner.de> > > > > What was there to test in this anyway? I see only comment change below. > > The full series was tested, irrespective of the content of the individual > patches. Tested-by's should be per patch, and in this patch tested-by has no meaning at all. In order to determine which patches tested-by is applicable it can be derived on what was actually tested. This looks as tested-by was used in place of acked/reviewed-by, which is not how it should be used. BR, Jarkko
diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c index 64e1e69d53ba..1814f009f971 100644 --- a/crypto/ecdsa.c +++ b/crypto/ecdsa.c @@ -122,7 +122,7 @@ static int _ecdsa_verify(struct ecc_ctx *ctx, const u64 *hash, const u64 *r, con /* res.x = res.x mod n (if res.x > order) */ if (unlikely(vli_cmp(res.x, curve->n, ndigits) == 1)) - /* faster alternative for NIST p384, p256 & p192 */ + /* faster alternative for NIST p521, p384, p256 & p192 */ vli_sub(res.x, res.x, curve->n, ndigits); if (!vli_cmp(res.x, r, ndigits))