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gpg: Create all MPIs with RFC-4880 correct length headers.

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* g10/build-packet.c (gpg_mpi_write): Strip leading zeroes.
--

This used not to work with opaque MPI as returned by Libgcrypt from
ECC operations.  This patch fixes this.

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2015-03-16 20:14:58 +01:00
parent bcc8250bc5
commit ab17f7b6c3
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GPG Key ID: E3FDFF218E45B72B
1 changed files with 19 additions and 1 deletions
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20
g10/build-packet.c
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@ -164,10 +164,28 @@ gpg_mpi_write (iobuf_t out, gcry_mpi_t a)
if (gcry_mpi_get_flag (a, GCRYMPI_FLAG_OPAQUE)) if (gcry_mpi_get_flag (a, GCRYMPI_FLAG_OPAQUE))
{ {
unsigned int nbits; unsigned int nbits;
const void *p; const unsigned char *p;
unsigned char lenhdr[2]; unsigned char lenhdr[2];
/* gcry_log_debugmpi ("a", a); */
p = gcry_mpi_get_opaque (a, &nbits); p = gcry_mpi_get_opaque (a, &nbits);
if (p)
{
/* 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;
}
/* gcry_log_debug (" [%u bit]\n", nbits); */
/* gcry_log_debughex (" ", p, (nbits+7)/8); */
lenhdr[0] = nbits >> 8; lenhdr[0] = nbits >> 8;
lenhdr[1] = nbits; lenhdr[1] = nbits;
rc = iobuf_write (out, lenhdr, 2); rc = iobuf_write (out, lenhdr, 2);