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g10: ECDH shared point format.
* g10/ecdh.c (pk_ecdh_encrypt_with_shared_point): Improve handling of ECDH shared point format. -- This handles the case where the result comes from scdaemon. Signed-off-by: Arnaud Fontaine <arnaud.fontaine at ssi.gouv.fr>
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32
g10/ecdh.c
32
g10/ecdh.c
@ -132,14 +132,30 @@ pk_ecdh_encrypt_with_shared_point (int is_encrypt, gcry_mpi_t shared_mpi,
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return err;
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}
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/* Expected size of the x component */
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secret_x_size = (nbits+7)/8;
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log_assert (nbytes >= secret_x_size);
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if ((nbytes & 1))
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/* Remove the "04" prefix of non-compressed format. */
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memmove (secret_x, secret_x+1, secret_x_size);
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if (nbytes - secret_x_size)
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memset (secret_x+secret_x_size, 0, nbytes-secret_x_size);
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if (nbytes > secret_x_size)
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{
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/* Uncompressed format expected, so it must start with 04 */
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if (secret_x[0] != (byte)0x04)
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{
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return gpg_error (GPG_ERR_BAD_DATA);
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}
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/* Remove the "04" prefix of non-compressed format. */
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memmove (secret_x, secret_x+1, secret_x_size);
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/* Zeroize the y component following */
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if (nbytes > secret_x_size)
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memset (secret_x+secret_x_size, 0, nbytes-secret_x_size);
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}
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else if (nbytes < secret_x_size)
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{
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/* Raw share secret (x coordinate), without leading zeros */
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memmove (secret_x+(secret_x_size - nbytes), secret_x, nbytes);
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memset (secret_x, 0, secret_x_size - nbytes);
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}
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if (DBG_CRYPTO)
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log_printhex ("ECDH shared secret X is:", secret_x, secret_x_size );
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}
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@ -235,8 +251,8 @@ pk_ecdh_encrypt_with_shared_point (int is_encrypt, gcry_mpi_t shared_mpi,
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return err;
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}
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gcry_md_write(h, "\x00\x00\x00\x01", 4); /* counter = 1 */
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gcry_md_write(h, secret_x, secret_x_size); /* x of the point X */
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gcry_md_write(h, message, message_size);/* KDF parameters */
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gcry_md_write(h, secret_x, secret_x_size); /* x of the point X */
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gcry_md_write(h, message, message_size); /* KDF parameters */
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gcry_md_final (h);
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