Add OpenSSL-compatible PKCS#5v1 KDF, demo of OpenSSL-compatible aes-256-cbc command.

crypt.tex

@@ -5070,6 +5070,8 @@ In order to securely handle user passwords for the purposes of creating session
 is made up of two algorithms, Algorithm One and Algorithm Two.  Algorithm One is the older fairly limited algorithm which has been implemented
 for completeness.  Algorithm Two is a bit more modern and more flexible to work with.
 
+The OpenSSL project implemented an extension to Algorithm One that allows for arbitrary keylengths; we have a compatible implementation described below.
+
 \subsection{Algorithm One}
 Algorithm One accepts as input a password, an 8--byte salt, and an iteration counter.  The iteration counter is meant to act as delay for
 people trying to brute force guess the password.  The higher the iteration counter the longer the delay.  This algorithm also requires a hash 
@@ -5092,6 +5094,17 @@ on the password.  The \textit{hash\_idx} is the index of the hash you wish to us
 The output of length up to \textit{outlen} is stored in \textit{out}.  If \textit{outlen} is initially larger than the size of the hash functions output
 it is set to the number of bytes stored.  If it is smaller than not all of the hash output is stored in \textit{out}.
 
+\index{pkcs\_5\_alg1\_openssl()}
+\begin{alltt}
+int pkcs_5_alg1_openssl(const unsigned char *password,
+                      unsigned long  password_len,
+                const unsigned char *salt,
+                                int  iteration_count,
+                                int  hash_idx,
+                      unsigned char *out,
+                      unsigned long *outlen)
+\end{alltt}
+As above, but we generate as many bytes as requested in outlen per the OpenSSL extension to Algorithm One.  If you are trying to be compatible with OpenSSL's EVP\_BytesToKey() or the "openssl enc" command line (or variants such as perl's Crypt::CBC), then use this function with MD5 as your hash (ick!) and iteration\_count=1 (double-ick!!).
 \subsection{Algorithm Two}
 
 Algorithm Two is the recommended algorithm for this task.  It allows variable length salts, and can produce outputs larger than the 

demos/openssl-enc.c

@@ -0,0 +1,381 @@
+/*
+ * Demo to do the rough equivalent of:
+ *
+ *    openssl enc -aes-256-cbc -pass pass:foobar -in infile -out outfile -p
+ *
+ * Compilation:
+ *
+ *    $(CC) -I /path/to/headers -L .../libs \
+ *          -o openssl-enc \
+ *          openssl-enc.c -ltomcrypt
+ *
+ * Usage:
+ *
+ *    ./openssl-enc <enc|dec> infile outfile "passphrase" [salt]
+ *
+ * If provided, the salt must be EXACTLY a 16-char hex string.
+ *
+ * Demo is an example of:
+ *
+ * - (When decrypting) yanking salt out of the OpenSSL "Salted__..." header
+ * - OpenSSL-compatible key derivation (in OpenSSL's modified PKCS#5v1 approach)
+ * - Grabbing an Initialization Vector from the key generator
+ * - Performing simple block encryption using AES
+ * - PKCS#7-type padding (which hopefully can get ripped out of this demo and
+ *   made a libtomcrypt thing someday).
+ *
+ * This program is free for all purposes without any express guarantee it
+ * works. If you really want to see a license here, assume the WTFPL :-)
+ *
+ * BJ Black, bblack@barracuda.com, https://wjblack.com
+ *
+ * BUGS:
+ *       Passing a password on a command line is a HORRIBLE idea.  Don't use
+ *       this program for serious work!
+ */
+
+#include <tomcrypt.h>
+
+#ifndef LTC_RIJNDAEL
+#error Cannot compile this demo; Rijndael (AES) required
+#endif
+#ifndef LTC_CBC_MODE
+#error Cannot compile this demo; CBC mode required
+#endif
+#ifndef LTC_PKCS_5
+#error Cannot compile this demo; PKCS5 required
+#endif
+#ifndef LTC_RNG_GET_BYTES
+#error Cannot compile this demo; random generator required
+#endif
+
+/* OpenSSL by default only runs one hash round */
+#define OPENSSL_ITERATIONS 1
+/* Use aes-256-cbc, so 256 bits of key, 128 of IV */
+#define KEY_LENGTH (256>>3)
+#define IV_LENGTH (128>>3)
+/* PKCS#5v1 requires exactly an 8-byte salt */
+#define SALT_LENGTH 8
+/* The header OpenSSL puts on an encrypted file */
+static char salt_header[] = { 'S', 'a', 'l', 't', 'e', 'd', '_', '_' };
+
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+
+/* A simple way to handle the possibility that a block may increase in size
+   after padding. */
+union paddable {
+   char unpad[1024];
+   char pad[1024+MAXBLOCKSIZE];
+};
+
+/*
+ * Print usage and exit with a bad status (and perror() if any errno).
+ *
+ * Input:        argv[0] and the error string
+ * Output:       <no return>
+ * Side Effects: print messages and barf (does exit(3))
+ */
+void barf(char *pname, char *err)
+{
+   printf("Usage: %s <enc|dec> infile outfile [salt]\n", pname);
+   printf("\n");
+   printf("       # encrypts infile->outfile, random salt\n");
+   printf("       %s enc infile outfile \"passphrase\"\n", pname);
+   printf("\n");
+   printf("       # encrypts infile->outfile, salt from cmdline\n");
+   printf("       %s enc infile outfile pass 0123456789abcdef\n", pname);
+   printf("\n");
+   printf("       # decrypts infile->outfile, pulls salt from infile\n");
+   printf("       %s dec infile outfile pass\n", pname);
+   printf("\n");
+   printf("       # decrypts infile->outfile, salt specified\n");
+   printf("       # (don't try to read the salt from infile)\n");
+   printf("       %s dec infile outfile pass 0123456789abcdef"
+          "\n", pname);
+   printf("\n");
+   printf("Application Error: %s\n", err);
+   if(errno)
+      perror("     System Error");
+   exit(-1);
+}
+
+/*
+ * Parse a salt value passed in on the cmdline.
+ *
+ * Input:        string passed in and a buf to put it in (exactly 8 bytes!)
+ * Output:       CRYPT_OK if parsed OK, CRYPT_ERROR if not
+ * Side Effects: none
+ */
+int parse_hex_salt(unsigned char *in, unsigned char *out)
+{
+   int idx;
+   for(idx=0; idx<SALT_LENGTH; idx++)
+      if(sscanf(in+idx*2, "%02hhx", out+idx) != 1)
+         return CRYPT_ERROR;
+   return CRYPT_OK;
+}
+
+/*
+ * Parse the Salted__[+8 bytes] from an OpenSSL-compatible file header.
+ *
+ * Input:        file to read from and a to put the salt in (exactly 8 bytes!)
+ * Output:       CRYPT_OK if parsed OK, CRYPT_ERROR if not
+ * Side Effects: infile's read pointer += 16
+ */
+int parse_openssl_header(FILE *in, unsigned char *out)
+{
+   unsigned char tmp[SALT_LENGTH];
+   if(fread(tmp, 1, sizeof(tmp), in) != sizeof(tmp))
+      return CRYPT_ERROR;
+   if(memcmp(tmp, salt_header, sizeof(tmp)))
+      return CRYPT_ERROR;
+   if(fread(tmp, 1, sizeof(tmp), in) != sizeof(tmp))
+      return CRYPT_ERROR;
+   memcpy(out, tmp, sizeof(tmp));
+   return CRYPT_OK;
+}
+
+/*
+ * Dump a hexed stream of bytes (convenience func).
+ *
+ * Input:        buf to read from, length
+ * Output:       none
+ * Side Effects: bytes printed as a hex blob, no lf at the end
+ */
+void dump_bytes(unsigned char *in, unsigned long len)
+{
+   unsigned long idx;
+   for(idx=0; idx<len; idx++)
+      printf("%02hhX", *(in+idx));
+}
+
+/*
+ * Pad or unpad a message using PKCS#7 padding.
+ * Padding will add 1-(blocksize) bytes and unpadding will remove that amount.
+ * Set is_padding to 1 to pad, 0 to unpad.
+ *
+ * Input:        paddable buffer, size read, block length of cipher, mode
+ * Output:       none
+ * Side Effects: bytes printed as a hex blob, no lf at the end
+ */
+size_t pkcs7_pad(union paddable *buf, size_t nb, int block_length,
+                 int is_padding)
+{
+   unsigned char padval;
+   off_t idx;
+
+   if(is_padding) {
+      /* We are PADDING this block (and therefore adding bytes) */
+      /* The pad value in PKCS#7 is the number of bytes remaining in
+         the block, so for a 16-byte block and 3 bytes left, it's
+         0x030303.  In the oddball case where nb is an exact multiple
+         multiple of block_length, set the padval to blocksize (i.e.
+         add one full block) */
+      padval = (unsigned char) (block_length - (nb % block_length));
+      padval = padval ? padval : block_length;
+
+      XMEMSET(buf->pad+nb, padval, padval);
+      return nb+padval;
+   } else {
+      /* We are UNPADDING this block (and removing bytes)
+         We really just need to verify that the pad bytes are correct,
+         so start at the end of the string and work backwards. */
+
+      /* Figure out what the padlength should be by looking at the
+         last byte */
+      idx = nb-1;
+      padval = buf->pad[idx];
+
+      /* padval must be nonzero and <= block length */
+      if(padval <= 0 || padval > block_length)
+         return -1;
+
+      /* First byte's accounted for; do the rest */
+      idx--;
+
+      while(idx >= nb-padval)
+         if(buf->pad[idx] != padval)
+            return -1;
+         else
+            idx--;
+
+      /* If we got here, the pad checked out, so return a smaller
+         number of bytes than nb (basically where we left off+1) */
+      return idx+1;
+   }
+}
+
+/*
+ * Perform an encrypt/decrypt operation to/from files using AES+CBC+PKCS7 pad.
+ * Set encrypt to 1 to encrypt, 0 to decrypt.
+ *
+ * Input:        in/out files, key, iv, and mode
+ * Output:       CRYPT_OK if no error
+ * Side Effects: bytes slurped from infile, pushed to outfile, fds updated.
+ */
+int do_crypt(FILE *infd, FILE *outfd, unsigned char *key, unsigned char *iv,
+             int encrypt)
+{
+   union paddable inbuf, outbuf;
+   int cipher, ret;
+   symmetric_CBC cbc;
+   size_t nb;
+
+   /* Register your cipher! */
+   cipher = register_cipher(&aes_desc);
+   if(cipher == -1)
+      return CRYPT_INVALID_CIPHER;
+
+   /* Start a CBC session with cipher/key/val params */
+   ret = cbc_start(cipher, iv, key, KEY_LENGTH, 0, &cbc);
+   if( ret != CRYPT_OK )
+      return -1;
+
+   do {
+      /* Get bytes from the source */
+      nb = fread(inbuf.unpad, 1, sizeof(inbuf.unpad), infd);
+      if(!nb)
+         return encrypt ? CRYPT_OK : CRYPT_ERROR;
+
+      /* Barf if we got a read error */
+      if(ferror(infd))
+         return CRYPT_ERROR;
+
+      if(encrypt) {
+         /* We're encrypting, so pad first (if at EOF) and then
+            crypt */
+         if(feof(infd))
+            nb = pkcs7_pad(&inbuf, nb,
+                           aes_desc.block_length, 1);
+
+         ret = cbc_encrypt(inbuf.pad, outbuf.pad, nb, &cbc);
+         if(ret != CRYPT_OK)
+            return ret;
+
+      } else {
+         /* We're decrypting, so decrypt and then unpad if at
+            EOF */
+         ret = cbc_decrypt(inbuf.unpad, outbuf.unpad, nb, &cbc);
+         if( ret != CRYPT_OK )
+            return ret;
+
+         if( feof(infd) )
+            nb = pkcs7_pad(&outbuf, nb,
+                           aes_desc.block_length, 0);
+         if(nb < 0)
+            /* The file didn't decrypt correctly */
+            return CRYPT_ERROR;
+
+      }
+
+      /* Push bytes to outfile */
+      if(fwrite(outbuf.unpad, 1, nb, outfd) != nb)
+         return CRYPT_ERROR;
+
+   } while(!feof(infd));
+
+   /* Close up */
+   cbc_done(&cbc);
+
+   return CRYPT_OK;
+}
+
+/* Convenience macro for the various barfable places below */
+#define BARF(a) { \
+   if(infd) fclose(infd); \
+   if(outfd) { fclose(outfd); remove(argv[3]); } \
+   barf(argv[0], a); \
+}
+/*
+ * The main routine.  Mostly validate cmdline params, open files, run the KDF,
+ * and do the crypt.
+ */
+int main(int argc, char *argv[]) {
+   unsigned char salt[SALT_LENGTH];
+   FILE *infd = NULL, *outfd = NULL;
+   int encrypt = -1;
+   int hash = -1;
+   int ret;
+   unsigned char keyiv[KEY_LENGTH + IV_LENGTH];
+   unsigned long keyivlen = (KEY_LENGTH + IV_LENGTH);
+   unsigned char *key, *iv;
+
+   /* Check proper number of cmdline args */
+   if(argc < 5 || argc > 6)
+      BARF("Invalid number of arguments");
+
+   /* Check proper mode of operation */
+   if     (!strncmp(argv[1], "enc", sizeof("enc")))
+      encrypt = 1;
+   else if(!strncmp(argv[1], "dec", sizeof("dec")))
+      encrypt = 0;
+   else
+      BARF("Bad command name");
+
+   /* Check we can open infile/outfile */
+   infd = fopen(argv[2], "rb");
+   if(infd == NULL)
+      BARF("Could not open infile");
+   outfd = fopen(argv[3], "wb");
+   if(outfd == NULL)
+      BARF("Could not open outfile");
+
+   /* Get the salt from wherever */
+   if(argc == 6) {
+      /* User-provided */
+      if(parse_hex_salt((unsigned char*) argv[5], salt) != CRYPT_OK)
+         BARF("Bad user-specified salt");
+   } else if(!strncmp(argv[1], "enc", sizeof("enc"))) {
+      /* Encrypting; get from RNG */
+      if(rng_get_bytes(salt, sizeof(salt), NULL) != sizeof(salt))
+         BARF("Not enough random data");
+   } else {
+      /* Parse from infile (decrypt only) */
+      if(parse_openssl_header(infd, salt) != CRYPT_OK)
+         BARF("Invalid OpenSSL header in infile");
+   }
+
+   /* Fetch the MD5 hasher for PKCS#5 */
+   hash = register_hash(&md5_desc);
+   if(hash == -1)
+      BARF("Could not register MD5 hash");
+
+   /* Set things to a sane initial state */
+   zeromem(keyiv, sizeof(keyiv));
+   key = keyiv + 0;      /* key comes first */
+   iv = keyiv + KEY_LENGTH;   /* iv comes next */
+
+   /* Run the key derivation from the provided passphrase.  This gets us
+      the key and iv. */
+   ret = pkcs_5_alg1_openssl(argv[4], strlen(argv[4]), salt,
+                             OPENSSL_ITERATIONS, hash, keyiv, &keyivlen );
+   if(ret != CRYPT_OK)
+      BARF("Could not derive key/iv from passphrase");
+
+   /* Display the salt/key/iv like OpenSSL cmdline does when -p */
+   printf("salt="); dump_bytes(salt, sizeof(salt)); printf("\n");
+   printf("key=");  dump_bytes(key, KEY_LENGTH);    printf("\n");
+   printf("iv =");  dump_bytes(iv,  IV_LENGTH );    printf("\n");
+
+   /* If we're encrypting, write the salt header as OpenSSL does */
+   if(!strncmp(argv[1], "enc", sizeof("enc"))) {
+      if(fwrite(salt_header, 1, sizeof(salt_header), outfd) !=
+         sizeof(salt_header) )
+         BARF("Error writing salt header to outfile");
+      if(fwrite(salt, 1, sizeof(salt), outfd) != sizeof(salt))
+         BARF("Error writing salt to outfile");
+   }
+
+   /* At this point, the files are open, the salt has been figured out,
+      and we're ready to pump data through crypt. */
+
+   /* Do the crypt operation */
+   if(do_crypt(infd, outfd, key, iv, encrypt) != CRYPT_OK)
+      BARF("Error during crypt operation");
+
+   /* Clean up */
+   fclose(infd); fclose(outfd);
+   return 0;
+}

src/headers/tomcrypt_pkcs.h

@@ -76,6 +76,14 @@ int pkcs_5_alg1(const unsigned char *password, unsigned long password_len,
                 int iteration_count,  int hash_idx,
                 unsigned char *out,   unsigned long *outlen);
 
+/* Algorithm #1 - OpenSSL-compatible variant for arbitrarily-long keys.
+   Compatible with EVP_BytesToKey() */
+int pkcs_5_alg1_openssl(const unsigned char *password,
+                        unsigned long password_len,
+                        const unsigned char *salt,
+                        int iteration_count,  int hash_idx,
+                        unsigned char *out,   unsigned long *outlen);
+
 /* Algorithm #2 (new) */
 int pkcs_5_alg2(const unsigned char *password, unsigned long password_len,
                 const unsigned char *salt,     unsigned long salt_len,

src/misc/pkcs5/pkcs_5_1.c

@@ -16,7 +16,17 @@
 */
 #ifdef LTC_PKCS_5
 /**
-   Execute PKCS #5 v1
+   Execute PKCS #5 v1 in strict or OpenSSL EVP_BytesToKey()-compat mode.
+
+   PKCS#5 v1 specifies that the output key length can be no larger than
+   the hash output length.  OpenSSL unilaterally extended that by repeating
+   the hash process on a block-by-block basis for as long as needed to make
+   bigger keys.  If you want to be compatible with KDF for e.g. "openssl enc",
+   you'll want that.
+
+   If you want strict PKCS behavior, turn openssl_compat off.  Or (more
+   likely), use one of the convenience functions below.
+
    @param password         The password (or key)
    @param password_len     The length of the password (octet)
    @param salt             The salt (or nonce) which is 8 octets long
@@ -24,17 +34,24 @@
    @param hash_idx         The index of the hash desired
    @param out              [out] The destination for this algorithm
    @param outlen           [in/out] The max size and resulting size of the algorithm output
+   @param openssl_compat   [in] Whether or not to grow the key to the buffer size ala OpenSSL
    @return CRYPT_OK if successful
 */
-int pkcs_5_alg1(const unsigned char *password, unsigned long password_len,
+static int _pkcs_5_alg1_common(const unsigned char *password,
+                       unsigned long password_len,
                        const unsigned char *salt,
                        int iteration_count,  int hash_idx,
-                unsigned char *out,   unsigned long *outlen)
+                       unsigned char *out,   unsigned long *outlen,
+                       int openssl_compat)
 {
    int err;
    unsigned long x;
    hash_state    *md;
    unsigned char *buf;
+   /* Storage vars in case we need to support > hashsize (OpenSSL compat) */
+   unsigned long block = 0, iter;
+   /* How many bytes to put in the outbut buffer (convenience calc) */
+   unsigned long outidx = 0, nb = 0;
 
    LTC_ARGCHK(password != NULL);
    LTC_ARGCHK(salt     != NULL);
@@ -59,10 +76,18 @@ int pkcs_5_alg1(const unsigned char *password, unsigned long password_len,
       return CRYPT_MEM;
    }
 
-   /* hash initial password + salt */
+   while(block * hash_descriptor[hash_idx].hashsize < *outlen) {
+
+      /* hash initial (maybe previous hash) + password + salt */
       if ((err = hash_descriptor[hash_idx].init(md)) != CRYPT_OK) {
           goto LBL_ERR;
       }
+      /* in OpenSSL mode, we first hash the previous result for blocks 2-n */
+      if (openssl_compat && block) {
+          if ((err = hash_descriptor[hash_idx].process(md, buf, hash_descriptor[hash_idx].hashsize)) != CRYPT_OK) {
+              goto LBL_ERR;
+          }
+      }
       if ((err = hash_descriptor[hash_idx].process(md, password, password_len)) != CRYPT_OK) {
           goto LBL_ERR;
       }
@@ -73,7 +98,8 @@ int pkcs_5_alg1(const unsigned char *password, unsigned long password_len,
           goto LBL_ERR;
       }
 
-   while (--iteration_count) {
+      iter = iteration_count;
+      while (--iter) {
          /* code goes here. */
          x = MAXBLOCKSIZE;
          if ((err = hash_memory(hash_idx, buf, hash_descriptor[hash_idx].hashsize, buf, &x)) != CRYPT_OK) {
@@ -81,11 +107,24 @@ int pkcs_5_alg1(const unsigned char *password, unsigned long password_len,
          }
       }
 
-   /* copy upto outlen bytes */
+      /* limit the size of the copy to however many bytes we have left in
-   for (x = 0; x < hash_descriptor[hash_idx].hashsize && x < *outlen; x++) {
+         the output buffer (and how many bytes we have to copy) */
-       out[x] = buf[x];
+      outidx = block*hash_descriptor[hash_idx].hashsize;
+      nb = hash_descriptor[hash_idx].hashsize;
+      if(outidx+nb > *outlen)
+          nb = *outlen - outidx;
+      if(nb > 0)
+          XMEMCPY(out+outidx, buf, nb);
+
+      block++;
+      if (!openssl_compat)
+          break;
    }
-   *outlen = x;
+   /* In strict mode, we always return the hashsize, in compat we filled it
+      as much as was requested, so we leave it alone. */
+   if(!openssl_compat)
+      *outlen = hash_descriptor[hash_idx].hashsize;
+
    err = CRYPT_OK;
 LBL_ERR:
 #ifdef LTC_CLEAN_STACK
@@ -99,6 +138,50 @@ LBL_ERR:
    return err;
 }
 
+/**
+   Execute PKCS #5 v1 - Strict mode (no OpenSSL-compatible extension)
+   @param password         The password (or key)
+   @param password_len     The length of the password (octet)
+   @param salt             The salt (or nonce) which is 8 octets long
+   @param iteration_count  The PKCS #5 v1 iteration count
+   @param hash_idx         The index of the hash desired
+   @param out              [out] The destination for this algorithm
+   @param outlen           [in/out] The max size and resulting size of the algorithm output
+   @return CRYPT_OK if successful
+*/
+int pkcs_5_alg1(const unsigned char *password, unsigned long password_len,
+                const unsigned char *salt,
+                int iteration_count,  int hash_idx,
+                unsigned char *out,   unsigned long *outlen)
+{
+   return _pkcs_5_alg1_common(password, password_len, salt, iteration_count,
+                             hash_idx, out, outlen, 0);
+}
+
+/**
+   Execute PKCS #5 v1 - OpenSSL-extension-compatible mode
+
+   Use this one if you need to derive keys as "openssl enc" does by default.
+   OpenSSL (for better or worse), uses MD5 as the hash and iteration_count=1.
+   @param password         The password (or key)
+   @param password_len     The length of the password (octet)
+   @param salt             The salt (or nonce) which is 8 octets long
+   @param iteration_count  The PKCS #5 v1 iteration count
+   @param hash_idx         The index of the hash desired
+   @param out              [out] The destination for this algorithm
+   @param outlen           [in/out] The max size and resulting size of the algorithm output
+   @return CRYPT_OK if successful
+*/
+int pkcs_5_alg1_openssl(const unsigned char *password,
+                        unsigned long password_len,
+                        const unsigned char *salt,
+                        int iteration_count,  int hash_idx,
+                        unsigned char *out,   unsigned long *outlen)
+{
+   return _pkcs_5_alg1_common(password, password_len, salt, iteration_count,
+                             hash_idx, out, outlen, 1);
+}
+
 #endif
 
 /* $Source$ */