359 lines
11 KiB
C
359 lines
11 KiB
C
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/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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/*
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* Demo to do the rough equivalent of:
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*
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* openssl enc -aes-256-cbc -pass pass:foobar -in infile -out outfile -p
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*
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* Compilation:
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*
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* $(CC) -I /path/to/headers -L .../libs \
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* -o openssl-enc \
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* openssl-enc.c -ltomcrypt
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*
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* Usage:
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*
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* ./openssl-enc <enc|dec> infile outfile "passphrase" [salt]
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*
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* If provided, the salt must be EXACTLY a 16-char hex string.
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*
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* Demo is an example of:
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*
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* - (When decrypting) yanking salt out of the OpenSSL "Salted__..." header
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* - OpenSSL-compatible key derivation (in OpenSSL's modified PKCS#5v1 approach)
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* - Grabbing an Initialization Vector from the key generator
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* - Performing simple block encryption using AES
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* - PKCS#7-type padding (which hopefully can get ripped out of this demo and
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* made a libtomcrypt thing someday).
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*
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* This program is free for all purposes without any express guarantee it
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* works. If you really want to see a license here, assume the WTFPL :-)
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*
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* BJ Black, bblack@barracuda.com, https://wjblack.com
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*
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* BUGS:
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* Passing a password on a command line is a HORRIBLE idea. Don't use
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* this program for serious work!
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*/
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#include <tomcrypt.h>
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#ifndef LTC_RIJNDAEL
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#error Cannot compile this demo; Rijndael (AES) required
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#endif
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#ifndef LTC_CBC_MODE
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#error Cannot compile this demo; CBC mode required
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#endif
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#ifndef LTC_PKCS_5
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#error Cannot compile this demo; PKCS5 required
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#endif
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#ifndef LTC_RNG_GET_BYTES
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#error Cannot compile this demo; random generator required
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#endif
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#ifndef LTC_MD5
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#error Cannot compile this demo; MD5 required
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#endif
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/* OpenSSL by default only runs one hash round */
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#define OPENSSL_ITERATIONS 1
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/* Use aes-256-cbc, so 256 bits of key, 128 of IV */
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#define KEY_LENGTH (256>>3)
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#define IV_LENGTH (128>>3)
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/* PKCS#5v1 requires exactly an 8-byte salt */
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#define SALT_LENGTH 8
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/* The header OpenSSL puts on an encrypted file */
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static char salt_header[] = { 'S', 'a', 'l', 't', 'e', 'd', '_', '_' };
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#include <errno.h>
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#include <stdio.h>
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#include <string.h>
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/* A simple way to handle the possibility that a block may increase in size
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after padding. */
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union paddable {
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unsigned char unpad[1024];
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unsigned char pad[1024+MAXBLOCKSIZE];
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};
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/*
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* Print usage and exit with a bad status (and perror() if any errno).
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*
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* Input: argv[0] and the error string
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* Output: <no return>
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* Side Effects: print messages and barf (does exit(3))
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*/
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void barf(const char *pname, const char *err)
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{
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printf("Usage: %s <enc|dec> infile outfile passphrase [salt]\n", pname);
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printf("\n");
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printf(" # encrypts infile->outfile, random salt\n");
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printf(" %s enc infile outfile \"passphrase\"\n", pname);
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printf("\n");
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printf(" # encrypts infile->outfile, salt from cmdline\n");
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printf(" %s enc infile outfile pass 0123456789abcdef\n", pname);
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printf("\n");
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printf(" # decrypts infile->outfile, pulls salt from infile\n");
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printf(" %s dec infile outfile pass\n", pname);
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printf("\n");
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printf(" # decrypts infile->outfile, salt specified\n");
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printf(" # (don't try to read the salt from infile)\n");
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printf(" %s dec infile outfile pass 0123456789abcdef"
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"\n", pname);
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printf("\n");
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printf("Application Error: %s\n", err);
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if(errno)
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perror(" System Error");
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exit(-1);
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}
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/*
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* Parse a salt value passed in on the cmdline.
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*
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* Input: string passed in and a buf to put it in (exactly 8 bytes!)
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* Output: CRYPT_OK if parsed OK, CRYPT_ERROR if not
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* Side Effects: none
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*/
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int parse_hex_salt(unsigned char *in, unsigned char *out)
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{
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int idx;
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for(idx=0; idx<SALT_LENGTH; idx++)
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if(sscanf((char*)in+idx*2, "%02hhx", out+idx) != 1)
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return CRYPT_ERROR;
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return CRYPT_OK;
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}
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/*
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* Parse the Salted__[+8 bytes] from an OpenSSL-compatible file header.
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*
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* Input: file to read from and a to put the salt in (exactly 8 bytes!)
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* Output: CRYPT_OK if parsed OK, CRYPT_ERROR if not
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* Side Effects: infile's read pointer += 16
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*/
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int parse_openssl_header(FILE *in, unsigned char *out)
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{
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unsigned char tmp[SALT_LENGTH];
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if(fread(tmp, 1, sizeof(tmp), in) != sizeof(tmp))
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return CRYPT_ERROR;
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if(memcmp(tmp, salt_header, sizeof(tmp)))
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return CRYPT_ERROR;
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if(fread(tmp, 1, sizeof(tmp), in) != sizeof(tmp))
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return CRYPT_ERROR;
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memcpy(out, tmp, sizeof(tmp));
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return CRYPT_OK;
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}
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/*
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* Dump a hexed stream of bytes (convenience func).
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*
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* Input: buf to read from, length
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* Output: none
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* Side Effects: bytes printed as a hex blob, no lf at the end
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*/
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void dump_bytes(unsigned char *in, unsigned long len)
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{
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unsigned long idx;
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for(idx=0; idx<len; idx++)
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printf("%02hhX", *(in+idx));
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}
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/*
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* Pad or unpad a message using PKCS#7 padding.
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* Padding will add 1-(blocksize) bytes and unpadding will remove that amount.
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* Set is_padding to 1 to pad, 0 to unpad.
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*
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* Input: paddable buffer, size read, block length of cipher, mode
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* Output: number of bytes after padding resp. after unpadding
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* Side Effects: none
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*/
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static size_t s_pkcs7_pad(union paddable *buf, size_t nb, int block_length,
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int is_padding)
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{
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unsigned long length;
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if(is_padding) {
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length = sizeof(buf->pad);
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if (padding_pad(buf->pad, nb, &length, block_length) != CRYPT_OK)
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return 0;
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return length;
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} else {
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length = nb;
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if (padding_depad(buf->pad, &length, 0) != CRYPT_OK)
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return 0;
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return length;
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}
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}
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/*
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* Perform an encrypt/decrypt operation to/from files using AES+CBC+PKCS7 pad.
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* Set encrypt to 1 to encrypt, 0 to decrypt.
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*
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* Input: in/out files, key, iv, and mode
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* Output: CRYPT_OK if no error
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* Side Effects: bytes slurped from infile, pushed to outfile, fds updated.
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*/
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int do_crypt(FILE *infd, FILE *outfd, unsigned char *key, unsigned char *iv,
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int encrypt)
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{
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union paddable inbuf, outbuf;
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int cipher, ret;
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symmetric_CBC cbc;
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size_t nb;
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/* Register your cipher! */
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cipher = register_cipher(&aes_desc);
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if(cipher == -1)
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return CRYPT_INVALID_CIPHER;
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/* Start a CBC session with cipher/key/val params */
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ret = cbc_start(cipher, iv, key, KEY_LENGTH, 0, &cbc);
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if( ret != CRYPT_OK )
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return -1;
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do {
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/* Get bytes from the source */
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nb = fread(inbuf.unpad, 1, sizeof(inbuf.unpad), infd);
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if(!nb)
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return encrypt ? CRYPT_OK : CRYPT_ERROR;
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/* Barf if we got a read error */
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if(ferror(infd))
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return CRYPT_ERROR;
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if(encrypt) {
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/* We're encrypting, so pad first (if at EOF) and then
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crypt */
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if(feof(infd))
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nb = s_pkcs7_pad(&inbuf, nb,
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aes_desc.block_length, 1);
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ret = cbc_encrypt(inbuf.pad, outbuf.pad, nb, &cbc);
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if(ret != CRYPT_OK)
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return ret;
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} else {
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/* We're decrypting, so decrypt and then unpad if at
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EOF */
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ret = cbc_decrypt(inbuf.unpad, outbuf.unpad, nb, &cbc);
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if( ret != CRYPT_OK )
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return ret;
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if(feof(infd))
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nb = s_pkcs7_pad(&outbuf, nb,
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aes_desc.block_length, 0);
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if(nb == 0)
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/* The file didn't decrypt correctly */
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return CRYPT_ERROR;
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}
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/* Push bytes to outfile */
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if(fwrite(outbuf.unpad, 1, nb, outfd) != nb)
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return CRYPT_ERROR;
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} while(!feof(infd));
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/* Close up */
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cbc_done(&cbc);
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return CRYPT_OK;
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}
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/* Convenience macro for the various barfable places below */
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#define BARF(a) { \
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if(infd) fclose(infd); \
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if(outfd) { fclose(outfd); remove(argv[3]); } \
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barf(argv[0], a); \
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}
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/*
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* The main routine. Mostly validate cmdline params, open files, run the KDF,
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* and do the crypt.
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*/
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int main(int argc, char *argv[]) {
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unsigned char salt[SALT_LENGTH];
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FILE *infd = NULL, *outfd = NULL;
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int encrypt = -1;
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int hash = -1;
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int ret;
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unsigned char keyiv[KEY_LENGTH + IV_LENGTH];
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unsigned long keyivlen = (KEY_LENGTH + IV_LENGTH);
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unsigned char *key, *iv;
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/* Check proper number of cmdline args */
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if(argc < 5 || argc > 6)
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BARF("Invalid number of arguments");
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/* Check proper mode of operation */
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if (!strncmp(argv[1], "enc", 3))
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encrypt = 1;
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else if(!strncmp(argv[1], "dec", 3))
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encrypt = 0;
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else
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BARF("Bad command name");
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/* Check we can open infile/outfile */
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infd = fopen(argv[2], "rb");
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if(infd == NULL)
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BARF("Could not open infile");
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outfd = fopen(argv[3], "wb");
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if(outfd == NULL)
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BARF("Could not open outfile");
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/* Get the salt from wherever */
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if(argc == 6) {
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/* User-provided */
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if(parse_hex_salt((unsigned char*) argv[5], salt) != CRYPT_OK)
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BARF("Bad user-specified salt");
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} else if(!strncmp(argv[1], "enc", 3)) {
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/* Encrypting; get from RNG */
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if(rng_get_bytes(salt, sizeof(salt), NULL) != sizeof(salt))
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BARF("Not enough random data");
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} else {
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/* Parse from infile (decrypt only) */
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if(parse_openssl_header(infd, salt) != CRYPT_OK)
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BARF("Invalid OpenSSL header in infile");
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}
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/* Fetch the MD5 hasher for PKCS#5 */
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hash = register_hash(&md5_desc);
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if(hash == -1)
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BARF("Could not register MD5 hash");
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/* Set things to a sane initial state */
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zeromem(keyiv, sizeof(keyiv));
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key = keyiv + 0; /* key comes first */
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iv = keyiv + KEY_LENGTH; /* iv comes next */
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/* Run the key derivation from the provided passphrase. This gets us
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the key and iv. */
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ret = pkcs_5_alg1_openssl((unsigned char*)argv[4], XSTRLEN(argv[4]), salt,
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OPENSSL_ITERATIONS, hash, keyiv, &keyivlen );
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if(ret != CRYPT_OK)
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BARF("Could not derive key/iv from passphrase");
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/* Display the salt/key/iv like OpenSSL cmdline does when -p */
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printf("salt="); dump_bytes(salt, sizeof(salt)); printf("\n");
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printf("key="); dump_bytes(key, KEY_LENGTH); printf("\n");
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printf("iv ="); dump_bytes(iv, IV_LENGTH ); printf("\n");
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/* If we're encrypting, write the salt header as OpenSSL does */
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if(!strncmp(argv[1], "enc", 3)) {
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if(fwrite(salt_header, 1, sizeof(salt_header), outfd) !=
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sizeof(salt_header) )
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BARF("Error writing salt header to outfile");
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if(fwrite(salt, 1, sizeof(salt), outfd) != sizeof(salt))
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BARF("Error writing salt to outfile");
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}
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/* At this point, the files are open, the salt has been figured out,
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and we're ready to pump data through crypt. */
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/* Do the crypt operation */
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if(do_crypt(infd, outfd, key, iv, encrypt) != CRYPT_OK)
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BARF("Error during crypt operation");
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/* Clean up */
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fclose(infd); fclose(outfd);
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return 0;
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}
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