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gpg: Emit compatible Ed25519 signature.

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* g10/pkglue.c (sexp_extract_param_sos_nlz): New.
* g10/pkglue.h: Add the declaration.
* g10/sign.c (do_sign): Use sexp_extract_param_sos_nlz for Ed25519.

--

Ed25519 signature in GnuPG 2.2 has no leading zeros.

GnuPG-bug-id: 5331
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
This commit is contained in:
NIIBE Yutaka 2021-12-10 15:39:32 +09:00
parent 426d82fcf1
commit 61ac580a20
3 changed files with 87 additions and 1 deletions
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79
g10/pkglue.c
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@ -47,8 +47,20 @@ get_mpi_from_sexp (gcry_sexp_t sexp, const char *item, int mpifmt)
}
/*
* SOS (Simply, Octet String) is an attempt to handle opaque octet
* string in OpenPGP, where well-formed MPI cannot represent octet
* string with leading zero octets.
*
* To retain maximum compatibility to existing MPI handling, SOS
* has same structure, but allows leading zero octets. When there
* is no leading zero octets, SOS representation is as same as MPI one.
* With leading zero octets, NBITS is 8*(length of octets), regardless
* of leading zero bits.
*/
/* Extract SOS representation from SEXP for PARAM, return the result
in R_SOS. */
* in R_SOS. It is represented by opaque MPI with GCRYMPI_FLAG_USER2
* flag. */
gpg_error_t
sexp_extract_param_sos (gcry_sexp_t sexp, const char *param, gcry_mpi_t *r_sos)
{
@ -98,6 +110,71 @@ sexp_extract_param_sos (gcry_sexp_t sexp, const char *param, gcry_mpi_t *r_sos)
}
/* "No leading zero octets" (nlz) version of the function above.
*
* This routine is used for backward compatibility to existing
* implementation with the weird handling of little endian integer
* representation with leading zero octets. For the sake of
* "well-fomed" MPI, which is designed for big endian integer, leading
* zero octets are removed when output, and they are recovered at
* input.
*
* Extract SOS representation from SEXP for PARAM, removing leading
* zeros, return the result in R_SOS. */
gpg_error_t
sexp_extract_param_sos_nlz (gcry_sexp_t sexp, const char *param,
gcry_mpi_t *r_sos)
{
gpg_error_t err;
gcry_sexp_t l2 = gcry_sexp_find_token (sexp, param, 0);
*r_sos = NULL;
if (!l2)
err = gpg_error (GPG_ERR_NO_OBJ);
else
{
size_t buflen;
const void *p0 = gcry_sexp_nth_data (l2, 1, &buflen);
if (!p0)
err = gpg_error_from_syserror ();
else
{
gcry_mpi_t sos;
unsigned int nbits = buflen*8;
const unsigned char *p = p0;
/* Strip leading zero bits. */
for (; nbits >= 8 && !*p; p++, nbits -= 8)
;
if (nbits >= 8 && !(*p & 0x80))
if (--nbits >= 7 && !(*p & 0x40))
if (--nbits >= 6 && !(*p & 0x20))
if (--nbits >= 5 && !(*p & 0x10))
if (--nbits >= 4 && !(*p & 0x08))
if (--nbits >= 3 && !(*p & 0x04))
if (--nbits >= 2 && !(*p & 0x02))
if (--nbits >= 1 && !(*p & 0x01))
--nbits;
sos = gcry_mpi_set_opaque_copy (NULL, p, nbits);
if (sos)
{
gcry_mpi_set_flag (sos, GCRYMPI_FLAG_USER2);
*r_sos = sos;
err = 0;
}
else
err = gpg_error_from_syserror ();
}
gcry_sexp_release (l2);
}
return err;
}
static byte *
get_data_from_sexp (gcry_sexp_t sexp, const char *item, size_t *r_size)
{