For NIST P192/256/384 the public key's x and y parameters could be copied
directly from a given array since both parameters filled 'ndigits' of
digits (a 'digit' is a u64). For support of NIST P521 the key parameters
first have to be copied into a temporary byte array with leading zeros
and can then be copied into the final digit array using ecc_swap_digits.
Implement ecc_digits_from_bytes to convert a byte array into an array of
digits and use this function in ecdsa_set_pub_key where an input byte array
needs to be converted into digits.
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
crypto/ecdsa.c | 14 +++++++++-----
include/crypto/internal/ecc.h | 19 +++++++++++++++++++
2 files changed, 28 insertions(+), 5 deletions(-)
diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c
index fbd76498aba8..ba8fb76fd165 100644
--- a/crypto/ecdsa.c
+++ b/crypto/ecdsa.c
@@ -222,9 +222,8 @@ static int ecdsa_ecc_ctx_reset(struct ecc_ctx *ctx)
static int ecdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key, unsigned int keylen)
{
struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+ unsigned int digitlen, ndigits;
const unsigned char *d = key;
- const u64 *digits = (const u64 *)&d[1];
- unsigned int ndigits;
int ret;
ret = ecdsa_ecc_ctx_reset(ctx);
@@ -238,12 +237,17 @@ static int ecdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key, unsig
return -EINVAL;
keylen--;
- ndigits = (keylen >> 1) / sizeof(u64);
+ digitlen = keylen >> 1;
+
+ ndigits = digitlen / sizeof(u64);
if (ndigits != ctx->curve->g.ndigits)
return -EINVAL;
- ecc_swap_digits(digits, ctx->pub_key.x, ndigits);
- ecc_swap_digits(&digits[ndigits], ctx->pub_key.y, ndigits);
+ d++;
+
+ ecc_digits_from_bytes(d, digitlen, ctx->pub_key.x, ndigits);
+ ecc_digits_from_bytes(&d[digitlen], digitlen, ctx->pub_key.y, ndigits);
+
ret = ecc_is_pubkey_valid_full(ctx->curve, &ctx->pub_key);
ctx->pub_key_set = ret == 0;
diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h
index 4f6c1a68882f..bee3329af7de 100644
--- a/include/crypto/internal/ecc.h
+++ b/include/crypto/internal/ecc.h
@@ -56,6 +56,25 @@ static inline void ecc_swap_digits(const void *in, u64 *out, unsigned int ndigit
out[i] = get_unaligned_be64(&src[ndigits - 1 - i]);
}
+/**
+ * ecc_digits_from_bytes() - Create ndigits-sized digits array from byte array
+ * @in: Input byte array
+ * @nbytes Size of input byte array
+ * @out Output digits array
+ * @ndigits: Number of digits to create from byte array
+ */
+static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
+ u64 *out, unsigned int ndigits)
+{
+ unsigned int sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
+ u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
+ unsigned int o = sz - nbytes;
+
+ memset(tmp, 0, o);
+ memcpy(&tmp[o], in, nbytes);
+ ecc_swap_digits(tmp, out, ndigits);
+}
+
/**
* ecc_is_key_valid() - Validate a given ECDH private key
*
--
2.43.0On Fri, Feb 23, 2024 at 03:41:40PM -0500, Stefan Berger wrote:
> +static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> + u64 *out, unsigned int ndigits)
> +{
> + unsigned int sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
> + u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
> + unsigned int o = sz - nbytes;
> +
> + memset(tmp, 0, o);
> + memcpy(&tmp[o], in, nbytes);
> + ecc_swap_digits(tmp, out, ndigits);
> +}
Copying the whole key into tmp seems inefficient. You only need
special handling for the first few bytes of "in" (6 bytes in the
P521 case) and could use ecc_swap_digits() to convert the rest
of "in" directly to "out" without using tmp.
So it would be sufficient to allocate the first digit on the stack,
memset + memcpy, then convert that to native byte order into "in[0]"
and use ecc_swap_digits() for the rest.
And the special handling would be conditional on "!o", so is skipped
for existing curves.
Thanks,
Lukas
On 2/29/24 04:11, Lukas Wunner wrote:
> On Fri, Feb 23, 2024 at 03:41:40PM -0500, Stefan Berger wrote:
>> +static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
>> + u64 *out, unsigned int ndigits)
>> +{
>> + unsigned int sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
>> + u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
>> + unsigned int o = sz - nbytes;
>> +
>> + memset(tmp, 0, o);
>> + memcpy(&tmp[o], in, nbytes);
>> + ecc_swap_digits(tmp, out, ndigits);
>> +}
>
> Copying the whole key into tmp seems inefficient. You only need
> special handling for the first few bytes of "in" (6 bytes in the
> P521 case) and could use ecc_swap_digits() to convert the rest
> of "in" directly to "out" without using tmp.
>
> So it would be sufficient to allocate the first digit on the stack,
> memset + memcpy, then convert that to native byte order into "in[0]"
> and use ecc_swap_digits() for the rest.
>
> And the special handling would be conditional on "!o", so is skipped
> for existing curves.
Thanks. It looks like this now:
static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
u64 *out, unsigned int ndigits)
{
unsigned int o = nbytes & 7;
u64 msd = 0;
size_t i;
if (o == 0) {
ecc_swap_digits(in, out, ndigits);
} else {
for (i = 0; i < o; i++)
msd = (msd << 8) | in[i];
out[ndigits - 1] = msd;
ecc_swap_digits(&in[o], out, ndigits - 1);
}
}
Stefan
>
> Thanks,
>
> Lukas
On Thu Feb 29, 2024 at 4:57 PM EET, Stefan Berger wrote:
>
>
> On 2/29/24 04:11, Lukas Wunner wrote:
> > On Fri, Feb 23, 2024 at 03:41:40PM -0500, Stefan Berger wrote:
> >> +static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> >> + u64 *out, unsigned int ndigits)
> >> +{
> >> + unsigned int sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
> >> + u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
> >> + unsigned int o = sz - nbytes;
> >> +
> >> + memset(tmp, 0, o);
> >> + memcpy(&tmp[o], in, nbytes);
> >> + ecc_swap_digits(tmp, out, ndigits);
> >> +}
> >
> > Copying the whole key into tmp seems inefficient. You only need
> > special handling for the first few bytes of "in" (6 bytes in the
> > P521 case) and could use ecc_swap_digits() to convert the rest
> > of "in" directly to "out" without using tmp.
> >
> > So it would be sufficient to allocate the first digit on the stack,
> > memset + memcpy, then convert that to native byte order into "in[0]"
> > and use ecc_swap_digits() for the rest.
> >
> > And the special handling would be conditional on "!o", so is skipped
> > for existing curves.
>
> Thanks. It looks like this now:
>
> static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> u64 *out, unsigned int ndigits)
> {
> unsigned int o = nbytes & 7;
> u64 msd = 0;
> size_t i;
>
> if (o == 0) {
> ecc_swap_digits(in, out, ndigits);
> } else {
> for (i = 0; i < o; i++)
> msd = (msd << 8) | in[i];
> out[ndigits - 1] = msd;
> ecc_swap_digits(&in[o], out, ndigits - 1);
This would be more stream-lined IMHO:
unsigned int o = nbytes & 7;
unsigned int n = ndigits;
u64 msd = 0;
size_t i;
if (o != 0) {
for (i = 0; i < o; i++)
msd = (msd << 8) | in[i];
out[--n] = msd;
}
ecc_swap_digits(in, out, n);
BR, Jarkko
On Fri, Mar 01, 2024 at 10:26:29PM +0200, Jarkko Sakkinen wrote:
> On Thu Feb 29, 2024 at 4:57 PM EET, Stefan Berger wrote:
> >
> >
> > On 2/29/24 04:11, Lukas Wunner wrote:
> > > On Fri, Feb 23, 2024 at 03:41:40PM -0500, Stefan Berger wrote:
> > >> +static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> > >> + u64 *out, unsigned int ndigits)
> > >> +{
> > >> + unsigned int sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
> > >> + u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
> > >> + unsigned int o = sz - nbytes;
> > >> +
> > >> + memset(tmp, 0, o);
> > >> + memcpy(&tmp[o], in, nbytes);
> > >> + ecc_swap_digits(tmp, out, ndigits);
> > >> +}
> > >
> > > Copying the whole key into tmp seems inefficient. You only need
> > > special handling for the first few bytes of "in" (6 bytes in the
> > > P521 case) and could use ecc_swap_digits() to convert the rest
> > > of "in" directly to "out" without using tmp.
> > >
> > > So it would be sufficient to allocate the first digit on the stack,
> > > memset + memcpy, then convert that to native byte order into "in[0]"
> > > and use ecc_swap_digits() for the rest.
> > >
> > > And the special handling would be conditional on "!o", so is skipped
> > > for existing curves.
> >
> > Thanks. It looks like this now:
> >
> > static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> > u64 *out, unsigned int ndigits)
> > {
> > unsigned int o = nbytes & 7;
> > u64 msd = 0;
> > size_t i;
> >
> > if (o == 0) {
> > ecc_swap_digits(in, out, ndigits);
> > } else {
> > for (i = 0; i < o; i++)
> > msd = (msd << 8) | in[i];
> > out[ndigits - 1] = msd;
> > ecc_swap_digits(&in[o], out, ndigits - 1);
>
> This would be more stream-lined IMHO:
>
> unsigned int o = nbytes & 7;
> unsigned int n = ndigits;
> u64 msd = 0;
> size_t i;
>
> if (o != 0) {
> for (i = 0; i < o; i++)
> msd = (msd << 8) | in[i];
>
> out[--n] = msd;
> }
>
> ecc_swap_digits(in, out, n);
Maybe eliminate the for-loop as well?
unsigned int o = nbytes & 7;
u64 msd = 0;
if (o != 0) {
/* if key length is not a multiple of 64 bits (NIST P521) */
memcpy((u8 *)&msd + sizeof(msd) - o, in, o);
out[--ndigits] = be64_to_cpu(msd);
in += o;
}
ecc_swap_digits(in, out, ndigits);
On Sat Mar 2, 2024 at 4:00 PM EET, Lukas Wunner wrote:
> On Fri, Mar 01, 2024 at 10:26:29PM +0200, Jarkko Sakkinen wrote:
> > On Thu Feb 29, 2024 at 4:57 PM EET, Stefan Berger wrote:
> > >
> > >
> > > On 2/29/24 04:11, Lukas Wunner wrote:
> > > > On Fri, Feb 23, 2024 at 03:41:40PM -0500, Stefan Berger wrote:
> > > >> +static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> > > >> + u64 *out, unsigned int ndigits)
> > > >> +{
> > > >> + unsigned int sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
> > > >> + u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
> > > >> + unsigned int o = sz - nbytes;
> > > >> +
> > > >> + memset(tmp, 0, o);
> > > >> + memcpy(&tmp[o], in, nbytes);
> > > >> + ecc_swap_digits(tmp, out, ndigits);
> > > >> +}
> > > >
> > > > Copying the whole key into tmp seems inefficient. You only need
> > > > special handling for the first few bytes of "in" (6 bytes in the
> > > > P521 case) and could use ecc_swap_digits() to convert the rest
> > > > of "in" directly to "out" without using tmp.
> > > >
> > > > So it would be sufficient to allocate the first digit on the stack,
> > > > memset + memcpy, then convert that to native byte order into "in[0]"
> > > > and use ecc_swap_digits() for the rest.
> > > >
> > > > And the special handling would be conditional on "!o", so is skipped
> > > > for existing curves.
> > >
> > > Thanks. It looks like this now:
> > >
> > > static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> > > u64 *out, unsigned int ndigits)
> > > {
> > > unsigned int o = nbytes & 7;
> > > u64 msd = 0;
> > > size_t i;
> > >
> > > if (o == 0) {
> > > ecc_swap_digits(in, out, ndigits);
> > > } else {
> > > for (i = 0; i < o; i++)
> > > msd = (msd << 8) | in[i];
> > > out[ndigits - 1] = msd;
> > > ecc_swap_digits(&in[o], out, ndigits - 1);
> >
> > This would be more stream-lined IMHO:
> >
> > unsigned int o = nbytes & 7;
> > unsigned int n = ndigits;
> > u64 msd = 0;
> > size_t i;
> >
> > if (o != 0) {
> > for (i = 0; i < o; i++)
> > msd = (msd << 8) | in[i];
> >
> > out[--n] = msd;
> > }
> >
> > ecc_swap_digits(in, out, n);
>
> Maybe eliminate the for-loop as well?
>
> unsigned int o = nbytes & 7;
> u64 msd = 0;
>
> if (o != 0) {
> /* if key length is not a multiple of 64 bits (NIST P521) */
> memcpy((u8 *)&msd + sizeof(msd) - o, in, o);
> out[--ndigits] = be64_to_cpu(msd);
> in += o;
> }
>
> ecc_swap_digits(in, out, ndigits);
+1
BR, Jarkko
On 3/2/24 09:00, Lukas Wunner wrote:
> On Fri, Mar 01, 2024 at 10:26:29PM +0200, Jarkko Sakkinen wrote:
>> On Thu Feb 29, 2024 at 4:57 PM EET, Stefan Berger wrote:
>>>
>>>
>>> On 2/29/24 04:11, Lukas Wunner wrote:
>>>> On Fri, Feb 23, 2024 at 03:41:40PM -0500, Stefan Berger wrote:
>>>>> +static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
>>>>> + u64 *out, unsigned int ndigits)
>>>>> +{
>>>>> + unsigned int sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
>>>>> + u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
>>>>> + unsigned int o = sz - nbytes;
>>>>> +
>>>>> + memset(tmp, 0, o);
>>>>> + memcpy(&tmp[o], in, nbytes);
>>>>> + ecc_swap_digits(tmp, out, ndigits);
>>>>> +}
>>>>
>>>> Copying the whole key into tmp seems inefficient. You only need
>>>> special handling for the first few bytes of "in" (6 bytes in the
>>>> P521 case) and could use ecc_swap_digits() to convert the rest
>>>> of "in" directly to "out" without using tmp.
>>>>
>>>> So it would be sufficient to allocate the first digit on the stack,
>>>> memset + memcpy, then convert that to native byte order into "in[0]"
>>>> and use ecc_swap_digits() for the rest.
>>>>
>>>> And the special handling would be conditional on "!o", so is skipped
>>>> for existing curves.
>>>
>>> Thanks. It looks like this now:
>>>
>>> static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
>>> u64 *out, unsigned int ndigits)
>>> {
>>> unsigned int o = nbytes & 7;
>>> u64 msd = 0;
>>> size_t i;
>>>
>>> if (o == 0) {
>>> ecc_swap_digits(in, out, ndigits);
>>> } else {
>>> for (i = 0; i < o; i++)
>>> msd = (msd << 8) | in[i];
>>> out[ndigits - 1] = msd;
>>> ecc_swap_digits(&in[o], out, ndigits - 1);
>>
>> This would be more stream-lined IMHO:
>>
>> unsigned int o = nbytes & 7;
>> unsigned int n = ndigits;
>> u64 msd = 0;
>> size_t i;
>>
>> if (o != 0) {
>> for (i = 0; i < o; i++)
>> msd = (msd << 8) | in[i];
>>
>> out[--n] = msd;
>> }
>>
>> ecc_swap_digits(in, out, n);
>
> Maybe eliminate the for-loop as well?
>
> unsigned int o = nbytes & 7;
> u64 msd = 0;
>
> if (o != 0) {
> /* if key length is not a multiple of 64 bits (NIST P521) */
> memcpy((u8 *)&msd + sizeof(msd) - o, in, o);
> out[--ndigits] = be64_to_cpu(msd);
> in += o;
> }
>
> ecc_swap_digits(in, out, ndigits);
>
Will take this for v5 with your Suggested-by:, ok?
Stefan
On Sat, Mar 02, 2024 at 04:19:49PM -0500, Stefan Berger wrote:
> On 3/2/24 09:00, Lukas Wunner wrote:
> > Maybe eliminate the for-loop as well?
> >
> > unsigned int o = nbytes & 7;
> > u64 msd = 0;
> >
> > if (o != 0) {
> > /* if key length is not a multiple of 64 bits (NIST P521) */
> > memcpy((u8 *)&msd + sizeof(msd) - o, in, o);
> > out[--ndigits] = be64_to_cpu(msd);
> > in += o;
> > }
> >
> > ecc_swap_digits(in, out, ndigits);
>
> Will take this for v5 with your Suggested-by:, ok?
Sure, feel free to, but better test it because I haven't. :-)
I'll look through the rest of the series tomorrow. %-)
Thanks,
Lukas
On 3/1/24 15:26, Jarkko Sakkinen wrote:
> On Thu Feb 29, 2024 at 4:57 PM EET, Stefan Berger wrote:
>>
>>
>> On 2/29/24 04:11, Lukas Wunner wrote:
>>> On Fri, Feb 23, 2024 at 03:41:40PM -0500, Stefan Berger wrote:
>>>> +static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
>>>> + u64 *out, unsigned int ndigits)
>>>> +{
>>>> + unsigned int sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
>>>> + u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
>>>> + unsigned int o = sz - nbytes;
>>>> +
>>>> + memset(tmp, 0, o);
>>>> + memcpy(&tmp[o], in, nbytes);
>>>> + ecc_swap_digits(tmp, out, ndigits);
>>>> +}
>>>
>>> Copying the whole key into tmp seems inefficient. You only need
>>> special handling for the first few bytes of "in" (6 bytes in the
>>> P521 case) and could use ecc_swap_digits() to convert the rest
>>> of "in" directly to "out" without using tmp.
>>>
>>> So it would be sufficient to allocate the first digit on the stack,
>>> memset + memcpy, then convert that to native byte order into "in[0]"
>>> and use ecc_swap_digits() for the rest.
>>>
>>> And the special handling would be conditional on "!o", so is skipped
>>> for existing curves.
>>
>> Thanks. It looks like this now:
>>
>> static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
>> u64 *out, unsigned int ndigits)
>> {
>> unsigned int o = nbytes & 7;
>> u64 msd = 0;
>> size_t i;
>>
>> if (o == 0) {
>> ecc_swap_digits(in, out, ndigits);
>> } else {
>> for (i = 0; i < o; i++)
>> msd = (msd << 8) | in[i];
>> out[ndigits - 1] = msd;
>> ecc_swap_digits(&in[o], out, ndigits - 1);
>
> This would be more stream-lined IMHO:
>
> unsigned int o = nbytes & 7;
> unsigned int n = ndigits;
> u64 msd = 0;
> size_t i;
>
> if (o != 0) {
> for (i = 0; i < o; i++)
> msd = (msd << 8) | in[i];
>
> out[--n] = msd;
> }
>
> ecc_swap_digits(in, out, n);
You forgot to advance 'in'.
>
> BR, Jarkko
>
On Fri Mar 1, 2024 at 10:48 PM EET, Stefan Berger wrote:
>
>
> On 3/1/24 15:26, Jarkko Sakkinen wrote:
> > On Thu Feb 29, 2024 at 4:57 PM EET, Stefan Berger wrote:
> >>
> >>
> >> On 2/29/24 04:11, Lukas Wunner wrote:
> >>> On Fri, Feb 23, 2024 at 03:41:40PM -0500, Stefan Berger wrote:
> >>>> +static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> >>>> + u64 *out, unsigned int ndigits)
> >>>> +{
> >>>> + unsigned int sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
> >>>> + u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
> >>>> + unsigned int o = sz - nbytes;
> >>>> +
> >>>> + memset(tmp, 0, o);
> >>>> + memcpy(&tmp[o], in, nbytes);
> >>>> + ecc_swap_digits(tmp, out, ndigits);
> >>>> +}
> >>>
> >>> Copying the whole key into tmp seems inefficient. You only need
> >>> special handling for the first few bytes of "in" (6 bytes in the
> >>> P521 case) and could use ecc_swap_digits() to convert the rest
> >>> of "in" directly to "out" without using tmp.
> >>>
> >>> So it would be sufficient to allocate the first digit on the stack,
> >>> memset + memcpy, then convert that to native byte order into "in[0]"
> >>> and use ecc_swap_digits() for the rest.
> >>>
> >>> And the special handling would be conditional on "!o", so is skipped
> >>> for existing curves.
> >>
> >> Thanks. It looks like this now:
> >>
> >> static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> >> u64 *out, unsigned int ndigits)
> >> {
> >> unsigned int o = nbytes & 7;
> >> u64 msd = 0;
> >> size_t i;
> >>
> >> if (o == 0) {
> >> ecc_swap_digits(in, out, ndigits);
> >> } else {
> >> for (i = 0; i < o; i++)
> >> msd = (msd << 8) | in[i];
> >> out[ndigits - 1] = msd;
> >> ecc_swap_digits(&in[o], out, ndigits - 1);
> >
> > This would be more stream-lined IMHO:
> >
> > unsigned int o = nbytes & 7;
> > unsigned int n = ndigits;
> > u64 msd = 0;
> > size_t i;
> >
> > if (o != 0) {
> > for (i = 0; i < o; i++)
> > msd = (msd << 8) | in[i];
> >
> > out[--n] = msd;
> > }
> >
> > ecc_swap_digits(in, out, n);
>
> You forgot to advance 'in'.
yeah, pointing out that two call sites is unnecessary complexity, that's
all
BR, Jarkko
On Thu, Feb 29, 2024 at 09:57:30AM -0500, Stefan Berger wrote:
> static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
> u64 *out, unsigned int ndigits)
> {
> unsigned int o = nbytes & 7;
> u64 msd = 0;
> size_t i;
>
> if (o == 0) {
> ecc_swap_digits(in, out, ndigits);
> } else {
> for (i = 0; i < o; i++)
> msd = (msd << 8) | in[i];
> out[ndigits - 1] = msd;
> ecc_swap_digits(&in[o], out, ndigits - 1);
> }
> }
Might be beneficial to add a code comment explaining the else-branch
is for curves with key length not a multiple of 64 bits (such as NIST P521).
Otherwise LGTM, thanks!
Lukas
On 2/29/24 11:48, Lukas Wunner wrote:
> On Thu, Feb 29, 2024 at 09:57:30AM -0500, Stefan Berger wrote:
>> static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
>> u64 *out, unsigned int ndigits)
>> {
>> unsigned int o = nbytes & 7;
>> u64 msd = 0;
>> size_t i;
>>
>> if (o == 0) {
>> ecc_swap_digits(in, out, ndigits);
>> } else {
>> for (i = 0; i < o; i++)
>> msd = (msd << 8) | in[i];
>> out[ndigits - 1] = msd;
>> ecc_swap_digits(&in[o], out, ndigits - 1);
>> }
>> }
>
> Might be beneficial to add a code comment explaining the else-branch
> is for curves with key length not a multiple of 64 bits (such as NIST P521).
Will do. I am also using this here now since it's safer:
ecc_swap_digits(&in[o], out, (nbytes - o) >> 3);
Stefan
>
> Otherwise LGTM, thanks!
>
> Lukas
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