diff options
Diffstat (limited to 'rsa-decrypt.c')
-rw-r--r-- | rsa-decrypt.c | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/rsa-decrypt.c b/rsa-decrypt.c new file mode 100644 index 00000000..a4cef7ad --- /dev/null +++ b/rsa-decrypt.c @@ -0,0 +1,75 @@ +/* rsa_decrypt.c + * + * The RSA publickey algorithm. PKCS#1 encryption. + */ + +/* nettle, low-level cryptographics library + * + * Copyright (C) 2001 Niels Möller + * + * The nettle library is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published by + * the Free Software Foundation; either version 2.1 of the License, or (at your + * option) any later version. + * + * The nettle library is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY + * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public + * License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with the nettle library; see the file COPYING.LIB. If not, write to + * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, + * MA 02111-1307, USA. + */ + +#include "rsa.h" + +#include "bignum.h" + +#include <assert.h> +#include <stdlib.h> +#include <string.h> + +int +rsa_decrypt(struct rsa_private_key *key, + unsigned *length, uint8_t *message, + const mpz_t gibberish) +{ + uint8_t *em; + uint8_t *terminator; + unsigned padding; + unsigned message_length; + + mpz_t m; + + mpz_init(m); + rsa_compute_root(key, m, gibberish); + + em = alloca(key->size); + nettle_mpz_get_str_256(key->size, em, m); + mpz_clear(m); + + /* Check format */ + if (em[0] || em[1] != 2) + return 0; + + terminator = memchr(em + 2, 0, key->size - 2); + + if (!terminator) + return 0; + + padding = terminator - (em + 2); + if (padding < 8) + return 0; + + message_length = key->size - 3 - padding; + + if (*length < message_length) + return 0; + + memcpy(message, terminator + 1, message_length); + *length = message_length; + + return 1; +} |