Adding upstream version 2.2.40.upstream/2.2.40upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 359 insertions, 0 deletions

diff --git a/g10/seskey.c b/g10/seskey.c
new file mode 100644
index 0000000..1549017
--- /dev/null
+++ b/g10/seskey.c
@@ -0,0 +1,359 @@
+/* seskey.c -  make session keys etc.
+ * Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004,
+ *               2006, 2009, 2010 Free Software Foundation, Inc.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG 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 3 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG 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, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "gpg.h"
+#include "../common/util.h"
+#include "options.h"
+#include "main.h"
+#include "../common/i18n.h"
+
+
+/* Generate a new session key in *DEK that is appropriate for the
+ * algorithm DEK->ALGO (i.e., ensure that the key is not weak).
+ *
+ * This function overwrites DEK->KEYLEN, DEK->KEY.  The rest of the
+ * fields are left as is.  */
+void
+make_session_key( DEK *dek )
+{
+    gcry_cipher_hd_t chd;
+    int i, rc;
+
+    dek->keylen = openpgp_cipher_get_algo_keylen (dek->algo);
+
+    if (openpgp_cipher_open (&chd, dek->algo, GCRY_CIPHER_MODE_CFB,
+			     (GCRY_CIPHER_SECURE
+			      | (dek->algo >= 100 ?
+				 0 : GCRY_CIPHER_ENABLE_SYNC))) )
+      BUG();
+    gcry_randomize (dek->key, dek->keylen, GCRY_STRONG_RANDOM );
+    for (i=0; i < 16; i++ )
+      {
+	rc = gcry_cipher_setkey (chd, dek->key, dek->keylen);
+	if (!rc)
+          {
+	    gcry_cipher_close (chd);
+	    return;
+          }
+        if (gpg_err_code (rc) != GPG_ERR_WEAK_KEY)
+          BUG();
+	log_info(_("weak key created - retrying\n") );
+	/* Renew the session key until we get a non-weak key. */
+	gcry_randomize (dek->key, dek->keylen, GCRY_STRONG_RANDOM);
+      }
+    log_fatal (_("cannot avoid weak key for symmetric cipher; "
+                 "tried %d times!\n"), i);
+}
+
+
+/* Encode the session key stored in DEK as an MPI in preparation to
+ * encrypt it with the public key algorithm OPENPGP_PK_ALGO with a key
+ * whose length (the size of the public key) is NBITS.
+ *
+ * On success, returns an MPI, which the caller must free using
+ * gcry_mpi_release().  */
+gcry_mpi_t
+encode_session_key (int openpgp_pk_algo, DEK *dek, unsigned int nbits)
+{
+  size_t nframe = (nbits+7) / 8;
+  byte *p;
+  byte *frame;
+  int i,n;
+  u16 csum;
+  gcry_mpi_t a;
+
+  if (DBG_CRYPTO)
+    log_debug ("encode_session_key: encoding %d byte DEK", dek->keylen);
+
+  csum = 0;
+  for (p = dek->key, i=0; i < dek->keylen; i++)
+    csum += *p++;
+
+  /* Shortcut for ECDH.  It's padding is minimal to simply make the
+     output be a multiple of 8 bytes.  */
+  if (openpgp_pk_algo == PUBKEY_ALGO_ECDH)
+    {
+      /* Pad to 8 byte granulatiry; the padding byte is the number of
+       * padded bytes.
+       *
+       * A  DEK(k bytes)  CSUM(2 bytes) 0x 0x 0x 0x ... 0x
+       *                                +---- x times ---+
+       */
+      nframe = (( 1 + dek->keylen + 2 /* The value so far is always odd. */
+                  + 7 ) & (~7));
+
+      /* alg+key+csum fit and the size is congruent to 8.  */
+      log_assert (!(nframe%8) && nframe > 1 + dek->keylen + 2 );
+
+      frame = xmalloc_secure (nframe);
+      n = 0;
+      frame[n++] = dek->algo;
+      memcpy (frame+n, dek->key, dek->keylen);
+      n += dek->keylen;
+      frame[n++] = csum >> 8;
+      frame[n++] = csum;
+      i = nframe - n;         /* Number of padded bytes.  */
+      memset (frame+n, i, i); /* Use it as the value of each padded byte.  */
+      log_assert (n+i == nframe);
+
+      if (DBG_CRYPTO)
+        log_debug ("encode_session_key: "
+                   "[%d] %02x  %02x %02x ...  %02x %02x %02x\n",
+                   (int) nframe, frame[0], frame[1], frame[2],
+                   frame[nframe-3], frame[nframe-2], frame[nframe-1]);
+
+      if (gcry_mpi_scan (&a, GCRYMPI_FMT_USG, frame, nframe, &nframe))
+        BUG();
+      xfree(frame);
+      return a;
+    }
+
+  /* The current limitation is that we can only use a session key
+   * whose length is a multiple of BITS_PER_MPI_LIMB
+   * I think we can live with that.
+   */
+  if (dek->keylen + 7 > nframe || !nframe)
+    log_bug ("can't encode a %d bit key in a %d bits frame\n",
+             dek->keylen*8, nbits );
+
+  /* We encode the session key according to PKCS#1 v1.5 (see section
+   * 13.1.1 of RFC 4880):
+   *
+   *	   0  2  RND(i bytes)  0  A  DEK(k bytes)  CSUM(2 bytes)
+   *
+   * (But how can we store the leading 0 - the external representaion
+   *  of MPIs doesn't allow leading zeroes =:-)
+   *
+   * RND are (at least 1) non-zero random bytes.
+   * A   is the cipher algorithm
+   * DEK is the encryption key (session key) length k depends on the
+   *	   cipher algorithm (20 is used with blowfish160).
+   * CSUM is the 16 bit checksum over the DEK
+   */
+
+  frame = xmalloc_secure( nframe );
+  n = 0;
+  frame[n++] = 0;
+  frame[n++] = 2;
+  /* The number of random bytes are the number of otherwise unused
+     bytes.  See diagram above.  */
+  i = nframe - 6 - dek->keylen;
+  log_assert( i > 0 );
+  p = gcry_random_bytes_secure (i, GCRY_STRONG_RANDOM);
+  /* Replace zero bytes by new values.  */
+  for (;;)
+    {
+      int j, k;
+      byte *pp;
+
+      /* Count the zero bytes. */
+      for (j=k=0; j < i; j++ )
+        if (!p[j])
+          k++;
+      if (!k)
+        break; /* Okay: no zero bytes. */
+      k += k/128 + 3; /* Better get some more. */
+      pp = gcry_random_bytes_secure (k, GCRY_STRONG_RANDOM);
+      for (j=0; j < i && k ;)
+        {
+          if (!p[j])
+            p[j] = pp[--k];
+          if (p[j])
+            j++;
+        }
+      xfree (pp);
+    }
+  memcpy (frame+n, p, i);
+  xfree (p);
+  n += i;
+  frame[n++] = 0;
+  frame[n++] = dek->algo;
+  memcpy (frame+n, dek->key, dek->keylen );
+  n += dek->keylen;
+  frame[n++] = csum >>8;
+  frame[n++] = csum;
+  log_assert (n == nframe);
+  if (gcry_mpi_scan( &a, GCRYMPI_FMT_USG, frame, n, &nframe))
+    BUG();
+  xfree (frame);
+  return a;
+}
+
+
+static gcry_mpi_t
+do_encode_md( gcry_md_hd_t md, int algo, size_t len, unsigned nbits,
+	      const byte *asn, size_t asnlen )
+{
+    size_t nframe = (nbits+7) / 8;
+    byte *frame;
+    int i,n;
+    gcry_mpi_t a;
+
+    if (len + asnlen + 4  > nframe)
+      {
+        log_error ("can't encode a %d bit MD into a %d bits frame, algo=%d\n",
+                   (int)(len*8), (int)nbits, algo);
+        return NULL;
+      }
+
+    /* We encode the MD in this way:
+     *
+     *	   0  1 PAD(n bytes)   0  ASN(asnlen bytes)  MD(len bytes)
+     *
+     * PAD consists of FF bytes.
+     */
+    frame = gcry_md_is_secure (md)? xmalloc_secure (nframe) : xmalloc (nframe);
+    n = 0;
+    frame[n++] = 0;
+    frame[n++] = 1; /* block type */
+    i = nframe - len - asnlen -3 ;
+    log_assert( i > 1 );
+    memset( frame+n, 0xff, i ); n += i;
+    frame[n++] = 0;
+    memcpy( frame+n, asn, asnlen ); n += asnlen;
+    memcpy( frame+n, gcry_md_read (md, algo), len ); n += len;
+    log_assert( n == nframe );
+
+    if (gcry_mpi_scan( &a, GCRYMPI_FMT_USG, frame, n, &nframe ))
+	BUG();
+    xfree(frame);
+
+    /* Note that PGP before version 2.3 encoded the MD as:
+     *
+     *   0   1   MD(16 bytes)   0   PAD(n bytes)   1
+     *
+     * The MD is always 16 bytes here because it's always MD5.  We do
+     * not support pre-v2.3 signatures, but I'm including this comment
+     * so the information is easily found in the future.
+     */
+
+    return a;
+}
+
+
+/****************
+ * Encode a message digest into an MPI.
+ * If it's for a DSA signature, make sure that the hash is large
+ * enough to fill up q.  If the hash is too big, take the leftmost
+ * bits.
+ */
+gcry_mpi_t
+encode_md_value (PKT_public_key *pk, gcry_md_hd_t md, int hash_algo)
+{
+  gcry_mpi_t frame;
+  size_t mdlen;
+
+  log_assert (hash_algo);
+  log_assert (pk);
+
+  if (pk->pubkey_algo == PUBKEY_ALGO_EDDSA)
+    {
+      /* EdDSA signs data of arbitrary length.  Thus no special
+         treatment is required.  */
+      frame = gcry_mpi_set_opaque_copy (NULL, gcry_md_read (md, hash_algo),
+                                        8*gcry_md_get_algo_dlen (hash_algo));
+    }
+  else if (pk->pubkey_algo == PUBKEY_ALGO_DSA
+           || pk->pubkey_algo == PUBKEY_ALGO_ECDSA)
+    {
+      /* It's a DSA signature, so find out the size of q.  */
+
+      size_t qbits = gcry_mpi_get_nbits (pk->pkey[1]);
+
+      /* pkey[1] is Q for ECDSA, which is an uncompressed point,
+         i.e.  04 <x> <y>  */
+      if (pk->pubkey_algo == PUBKEY_ALGO_ECDSA)
+        qbits = ecdsa_qbits_from_Q (qbits);
+
+      /* Make sure it is a multiple of 8 bits. */
+      if ((qbits%8))
+	{
+	  log_error(_("DSA requires the hash length to be a"
+		      " multiple of 8 bits\n"));
+	  return NULL;
+	}
+
+      /* Don't allow any q smaller than 160 bits.  This might need a
+	 revisit as the DSA2 design firms up, but for now, we don't
+	 want someone to issue signatures from a key with a 16-bit q
+	 or something like that, which would look correct but allow
+	 trivial forgeries.  Yes, I know this rules out using MD5 with
+	 DSA. ;) */
+      if (qbits < 160)
+	{
+	  log_error (_("%s key %s uses an unsafe (%zu bit) hash\n"),
+                     openpgp_pk_algo_name (pk->pubkey_algo),
+                     keystr_from_pk (pk), qbits);
+	  return NULL;
+	}
+
+
+      /* ECDSA 521 is special has it is larger than the largest hash
+         we have (SHA-512).  Thus we change the size for further
+         processing to 512.  */
+      if (pk->pubkey_algo == PUBKEY_ALGO_ECDSA && qbits > 512)
+        qbits = 512;
+
+      /* Check if we're too short.  Too long is safe as we'll
+	 automatically left-truncate.  */
+      mdlen = gcry_md_get_algo_dlen (hash_algo);
+      if (mdlen < qbits/8)
+	{
+	  log_error (_("%s key %s requires a %zu bit or larger hash "
+                       "(hash is %s)\n"),
+                     openpgp_pk_algo_name (pk->pubkey_algo),
+                     keystr_from_pk (pk), qbits,
+                     gcry_md_algo_name (hash_algo));
+	  return NULL;
+	}
+
+     /* Note that we do the truncation by passing QBITS/8 as length to
+        mpi_scan.  */
+      if (gcry_mpi_scan (&frame, GCRYMPI_FMT_USG,
+                         gcry_md_read (md, hash_algo), qbits/8, NULL))
+        BUG();
+    }
+  else
+    {
+      gpg_error_t rc;
+      byte *asn;
+      size_t asnlen;
+
+      rc = gcry_md_algo_info (hash_algo, GCRYCTL_GET_ASNOID, NULL, &asnlen);
+      if (rc)
+        log_fatal ("can't get OID of digest algorithm %d: %s\n",
+                   hash_algo, gpg_strerror (rc));
+      asn = xtrymalloc (asnlen);
+      if (!asn)
+        return NULL;
+      if ( gcry_md_algo_info (hash_algo, GCRYCTL_GET_ASNOID, asn, &asnlen) )
+        BUG();
+      frame = do_encode_md (md, hash_algo, gcry_md_get_algo_dlen (hash_algo),
+                            gcry_mpi_get_nbits (pk->pkey[0]), asn, asnlen);
+      xfree (asn);
+    }
+
+  return frame;
+}