Implement CFB with 8-bit mode

* cipher/cipher-cfb.c (_gcry_cipher_cfb8_encrypt)
(_gcry_cipher_cfg8_decrypt): Add 8-bit variants of decrypt/encrypt
functions.
* cipher/cipher-internal.h (_gcry_cipher_cfb8_encrypt)
(_gcry_cipher_cfg8_decrypt): Ditto.
* cipher/cipher.c: Adjust code flow to work with GCRY_CIPHER_MODE_CFB8.
* tests/basic.c: Add tests for cfb8 with AES and 3DES.
--

Signed-off-by: Mathias L. Baumann <mathias.baumann at sociomantic.com>
[JK: edit changelog, fix email malformed patch]
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>

3 files changed, 103 insertions, 0 deletions

diff --git a/cipher/cipher-cfb.c b/cipher/cipher-cfb.c
index 21c81ca2..cca5c1fb 100644
--- a/cipher/cipher-cfb.c
+++ b/cipher/cipher-cfb.c
@@ -233,3 +233,89 @@ _gcry_cipher_cfb_decrypt (gcry_cipher_hd_t c,
 
   return 0;
 }
+
+
+gcry_err_code_t
+_gcry_cipher_cfb8_encrypt (gcry_cipher_hd_t c,
+                          unsigned char *outbuf, size_t outbuflen,
+                          const unsigned char *inbuf, size_t inbuflen)
+{
+  gcry_cipher_encrypt_t enc_fn = c->spec->encrypt;
+  size_t blocksize = c->spec->blocksize;
+  unsigned int burn, nburn;
+
+  if (outbuflen < inbuflen)
+    return GPG_ERR_BUFFER_TOO_SHORT;
+
+  burn = 0;
+
+  while ( inbuflen > 0)
+    {
+      /* Encrypt the IV. */
+      nburn = enc_fn ( &c->context.c, c->lastiv, c->u_iv.iv );
+      burn = nburn > burn ? nburn : burn;
+
+      outbuf[0] = c->lastiv[0] ^ inbuf[0];
+
+      /* Bitshift iv by 8 bit to the left */
+      for (int i = 0; i < blocksize-1; i++)
+        c->u_iv.iv[i] = c->u_iv.iv[i+1];
+
+      /* append cipher text to iv */
+      c->u_iv.iv[blocksize-1] = outbuf[0];
+
+      outbuf += 1;
+      inbuf += 1;
+      inbuflen -= 1;
+    }
+
+  if (burn > 0)
+    _gcry_burn_stack (burn + 4 * sizeof(void *));
+
+  return 0;
+}
+
+
+gcry_err_code_t
+_gcry_cipher_cfb8_decrypt (gcry_cipher_hd_t c,
+                          unsigned char *outbuf, size_t outbuflen,
+                          const unsigned char *inbuf, size_t inbuflen)
+{
+  gcry_cipher_encrypt_t enc_fn = c->spec->encrypt;
+  size_t blocksize = c->spec->blocksize;
+  unsigned int burn, nburn;
+  unsigned char appendee;
+
+  if (outbuflen < inbuflen)
+    return GPG_ERR_BUFFER_TOO_SHORT;
+
+  burn = 0;
+
+  while (inbuflen > 0)
+    {
+      /* Encrypt the IV. */
+      nburn = enc_fn ( &c->context.c, c->lastiv, c->u_iv.iv );
+      burn = nburn > burn ? nburn : burn;
+
+      /* inbuf might == outbuf, make sure we keep the value
+         so we can append it later */
+      appendee = inbuf[0];
+
+      outbuf[0] = inbuf[0] ^ c->lastiv[0];
+
+      /* Bitshift iv by 8 bit to the left */
+      for (int i = 0; i < blocksize-1; i++)
+        c->u_iv.iv[i] = c->u_iv.iv[i+1];
+
+      c->u_iv.iv[blocksize-1] = appendee;
+
+      outbuf += 1;
+      inbuf += 1;
+      inbuflen -= 1;
+    }
+
+  if (burn > 0)
+    _gcry_burn_stack (burn + 4 * sizeof(void *));
+
+  return 0;
+}
diff --git a/cipher/cipher-internal.h b/cipher/cipher-internal.h
index 33d0629c..ea9c33d3 100644
--- a/cipher/cipher-internal.h
+++ b/cipher/cipher-internal.h
@@ -348,6 +348,14 @@ gcry_err_code_t _gcry_cipher_cfb_decrypt
 /*           */ (gcry_cipher_hd_t c,
                  unsigned char *outbuf, size_t outbuflen,
                  const unsigned char *inbuf, size_t inbuflen);
+gcry_err_code_t _gcry_cipher_cfb8_encrypt
+/*           */ (gcry_cipher_hd_t c,
+                 unsigned char *outbuf, size_t outbuflen,
+                 const unsigned char *inbuf, size_t inbuflen);
+gcry_err_code_t _gcry_cipher_cfb8_decrypt
+/*           */ (gcry_cipher_hd_t c,
+                 unsigned char *outbuf, size_t outbuflen,
+                 const unsigned char *inbuf, size_t inbuflen);
 
 
 /*-- cipher-ofb.c --*/
diff --git a/cipher/cipher.c b/cipher/cipher.c
index 06ce1dad..124700e9 100644
--- a/cipher/cipher.c
+++ b/cipher/cipher.c
@@ -415,6 +415,7 @@ _gcry_cipher_open_internal (gcry_cipher_hd_t *handle,
       case GCRY_CIPHER_MODE_ECB:
       case GCRY_CIPHER_MODE_CBC:
       case GCRY_CIPHER_MODE_CFB:
+      case GCRY_CIPHER_MODE_CFB8:
       case GCRY_CIPHER_MODE_OFB:
       case GCRY_CIPHER_MODE_CTR:
       case GCRY_CIPHER_MODE_AESWRAP:
@@ -902,6 +903,10 @@ cipher_encrypt (gcry_cipher_hd_t c, byte *outbuf, size_t outbuflen,
       rc = _gcry_cipher_cfb_encrypt (c, outbuf, outbuflen, inbuf, inbuflen);
       break;
 
+    case GCRY_CIPHER_MODE_CFB8:
+      rc = _gcry_cipher_cfb8_encrypt (c, outbuf, outbuflen, inbuf, inbuflen);
+      break;
+
     case GCRY_CIPHER_MODE_OFB:
       rc = _gcry_cipher_ofb_encrypt (c, outbuf, outbuflen, inbuf, inbuflen);
       break;
@@ -1029,6 +1034,10 @@ cipher_decrypt (gcry_cipher_hd_t c, byte *outbuf, size_t outbuflen,
       rc = _gcry_cipher_cfb_decrypt (c, outbuf, outbuflen, inbuf, inbuflen);
       break;
 
+    case GCRY_CIPHER_MODE_CFB8:
+      rc = _gcry_cipher_cfb8_decrypt (c, outbuf, outbuflen, inbuf, inbuflen);
+      break;
+
     case GCRY_CIPHER_MODE_OFB:
       rc = _gcry_cipher_ofb_encrypt (c, outbuf, outbuflen, inbuf, inbuflen);
       break;