Add gcry_cipher_ctl command to allow weak keys in testing use-cases

* cipher/cipher-internal.h (gcry_cipher_handle): Add
'marks.allow_weak_key' flag.
* cipher/cipher.c (cipher_setkey): Do not handle weak key as error when
weak keys are allowed.
(cipher_reset): Preserve 'marks.allow_weak_key' flag on object reset.
(_gcry_cipher_ctl): Add handling for GCRYCTL_SET_ALLOW_WEAK_KEY.
* src/gcrypt.h.in (gcry_ctl_cmds): Add GCRYCTL_SET_ALLOW_WEAK_KEY.
* tests/basic.c (check_ecb_cipher): Add tests for weak key errors and
for GCRYCTL_SET_ALLOW_WEAK_KEY.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>

2 files changed, 13 insertions, 3 deletions

diff --git a/cipher/cipher-internal.h b/cipher/cipher-internal.h
index 47b7b6f9..262ca902 100644
--- a/cipher/cipher-internal.h
+++ b/cipher/cipher-internal.h
@@ -207,6 +207,7 @@ struct gcry_cipher_handle
     unsigned int iv:1;  /* Set to 1 if a IV has been set.  */
     unsigned int tag:1; /* Set to 1 if a tag is finalized. */
     unsigned int finalize:1; /* Next encrypt/decrypt has the final data.  */
+    unsigned int allow_weak_key:1; /* Set to 1 if weak keys are allowed. */
   } marks;
 
   /* The initialization vector.  For best performance we make sure
diff --git a/cipher/cipher.c b/cipher/cipher.c
index bd571367..09b8d829 100644
--- a/cipher/cipher.c
+++ b/cipher/cipher.c
@@ -794,7 +794,7 @@ cipher_setkey (gcry_cipher_hd_t c, byte *key, size_t keylen)
     }
 
   rc = c->spec->setkey (&c->context.c, key, keylen, c);
-  if (!rc)
+  if (!rc || (c->marks.allow_weak_key && rc == GPG_ERR_WEAK_KEY))
     {
       /* Duplicate initial context.  */
       memcpy ((void *) ((char *) &c->context.c + c->spec->contextsize),
@@ -828,7 +828,7 @@ cipher_setkey (gcry_cipher_hd_t c, byte *key, size_t keylen)
 	  /* Setup tweak cipher with second part of XTS key. */
 	  rc = c->spec->setkey (c->u_mode.xts.tweak_context, key + keylen,
 				keylen, c);
-	  if (!rc)
+	  if (!rc || (c->marks.allow_weak_key && rc == GPG_ERR_WEAK_KEY))
 	    {
 	      /* Duplicate initial tweak context.  */
 	      memcpy (c->u_mode.xts.tweak_context + c->spec->contextsize,
@@ -889,9 +889,10 @@ cipher_setiv (gcry_cipher_hd_t c, const byte *iv, size_t ivlen)
 static void
 cipher_reset (gcry_cipher_hd_t c)
 {
-  unsigned int marks_key;
+  unsigned int marks_key, marks_allow_weak_key;
 
   marks_key = c->marks.key;
+  marks_allow_weak_key = c->marks.allow_weak_key;
 
   memcpy (&c->context.c,
 	  (char *) &c->context.c + c->spec->contextsize,
@@ -903,6 +904,7 @@ cipher_reset (gcry_cipher_hd_t c)
   c->unused = 0;
 
   c->marks.key = marks_key;
+  c->marks.allow_weak_key = marks_allow_weak_key;
 
   switch (c->mode)
     {
@@ -1592,6 +1594,13 @@ _gcry_cipher_ctl (gcry_cipher_hd_t h, int cmd, void *buffer, size_t buflen)
         rc = GPG_ERR_NOT_SUPPORTED;
       break;
 
+    case GCRYCTL_SET_ALLOW_WEAK_KEY:
+      /* Expecting BUFFER to be NULL and buflen to be on/off flag (0 or 1). */
+      if (!h || buffer || buflen > 1)
+	return GPG_ERR_CIPHER_ALGO;
+      h->marks.allow_weak_key = buflen ? 1 : 0;
+      break;
+
     default:
       rc = GPG_ERR_INV_OP;
     }