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Diffstat (limited to 'g10/pubkey-enc.c')
| -rw-r--r-- | g10/pubkey-enc.c | 130 |
1 files changed, 130 insertions, 0 deletions
diff --git a/g10/pubkey-enc.c b/g10/pubkey-enc.c new file mode 100644 index 000000000..18c737c2d --- /dev/null +++ b/g10/pubkey-enc.c @@ -0,0 +1,130 @@ +/* pubkey-enc.c - public key encoded packet handling + * Copyright (c) 1997 by Werner Koch (dd9jn) + * + * This file is part of G10. + * + * G10 is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * G10 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA + */ + +#include <config.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <assert.h> +#include "util.h" +#include "memory.h" +#include "packet.h" +#include "mpi.h" +#include "keydb.h" +#include "cipher.h" + + +/**************** + * Get the session key from a pubkey enc paket and return + * it in DEK, which should have been allocated in secure memory. + */ +int +get_session_key( PKT_pubkey_enc *k, DEK *dek ) +{ + int i, j, c, rc = 0; + RSA_secret_key *skey = m_alloc_secure( sizeof *skey ); + MPI dek_frame = mpi_alloc_secure(40); + u16 csum, csum2; + + if( k->pubkey_algo != PUBKEY_ALGO_RSA ) { + rc = G10ERR_PUBKEY_ALGO; /* unsupported algorithm */ + goto leave; + } + + /* get the secret key for the given public key + * and decode the rsa_integer + */ + if( (rc = get_seckey( skey, k->keyid )) ) + goto leave; + + if( DBG_CIPHER ) + log_mpidump("Encr DEK frame:", k->d.rsa.rsa_integer ); + rsa_secret( dek_frame, k->d.rsa.rsa_integer, skey ); + /* Now get the DEK (data encryption key) from the dek_frame + * + * Old versions encode the DEK in in this format (msb is left): + * + * 0 1 DEK(16 bytes) CSUM(2 bytes) 0 RND(n bytes) 2 + * + * Later versions encode the DEK like this: + * + * 0 2 RND(n bytes) 0 A DEK(k bytes) CSUM(2 bytes) + * + * RND are non-zero randow bytes. + * A is the cipher algorithm ( 1 for IDEA, 42 for blowfish ) + * DEK is the encryption key (session key) with length k + * (16 for idea, 42 for blowfish) + * CSUM + */ + if( DBG_CIPHER ) + log_mpidump("DEK frame:", dek_frame ); + for(i=0; mpi_getbyte(dek_frame, i) != -1; i++ ) + ; + for(i--; i >= 0 && !(c=mpi_getbyte(dek_frame, i)); i--) + ; /* Skip leading zeroes */ + if( i < 16 ) + { rc = G10ERR_WRONG_SECKEY; goto leave; } + if( c == 1 && mpi_getbyte(dek_frame,0) == 2 ) { + log_error("old encoding of DEK is not supported\n"); + rc = G10ERR_CIPHER_ALGO; + goto leave; + } + if( c != 2 ) /* somethink is wrong */ + { rc = G10ERR_WRONG_SECKEY; goto leave; } + /* look for the zeor byte */ + for(i--; i > 4 ; i-- ) + if( !mpi_getbyte(dek_frame,i) ) + break; + if( i <= 4 ) /* zero byte not found */ + { rc = G10ERR_WRONG_SECKEY; goto leave; } + /* next byte indicates the used cipher */ + switch( mpi_getbyte(dek_frame, --i ) ) { + case 1: + rc = G10ERR_NI_CIPHER; + goto leave; + case 42: + if( i != 22 ) /* length of blowfish is 20 (+2 bytes checksum) */ + { rc = G10ERR_WRONG_SECKEY; goto leave; } + dek->algo = CIPHER_ALGO_BLOWFISH; + break; + default: + rc = G10ERR_CIPHER_ALGO; + goto leave; + } + /* copy the key to DEK and compare the checksum */ + csum = mpi_getbyte(dek_frame, 1) << 8; + csum |= mpi_getbyte(dek_frame, 0); + dek->keylen = i - 2; + for( i--, csum2=0, j=0; i > 1; i-- ) + csum2 += dek->key[j++] = mpi_getbyte(dek_frame, i); + if( csum != csum2 ) { + rc = G10ERR_WRONG_SECKEY; + goto leave; + } + if( DBG_CIPHER ) + log_hexdump("DEK is:", dek->key, dek->keylen ); + + leave: + mpi_free(dek_frame); + m_free(skey); + return rc; +} + + |