md: add variable length output interface

* cipher/crc.c (_gcry_digest_spec_crc32)
(_gcry_digest_spec_crc32_rfc1510, _gcry_digest_spec_crc24_rfc2440): Set
'extract' NULL.
* cipher/gostr3411-94.c (_gcry_digest_spec_gost3411_94)
(_gcry_digest_spec_gost3411_cp): Ditto.
* cipher/keccak.c (_gcry_digest_spec_sha3_224)
(_gcry_digest_spec_sha3_256, _gcry_digest_spec_sha3_384)
(_gcry_digest_spec_sha3_512): Ditto.
* cipher/md2.c (_gcry_digest_spec_md2): Ditto.
* cipher/md4.c (_gcry_digest_spec_md4): Ditto.
* cipher/md5.c (_gcry_digest_spec_md5): Ditto.
* cipher/rmd160.c (_gcry_digest_spec_rmd160): Ditto.
* cipher/sha1.c (_gcry_digest_spec_sha1): Ditto.
* cipher/sha256.c (_gcry_digest_spec_sha224)
(_gcry_digest_spec_sha256): Ditto.
* cipher/sha512.c (_gcry_digest_spec_sha384)
(_gcry_digest_spec_sha512): Ditto.
* cipher/stribog.c (_gcry_digest_spec_stribog_256)
(_gcry_digest_spec_stribog_512): Ditto.
* cipher/tiger.c (_gcry_digest_spec_tiger)
(_gcry_digest_spec_tiger1, _gcry_digest_spec_tiger2): Ditto.
* cipher/whirlpool.c (_gcry_digest_spec_whirlpool): Ditto.
* cipher/md.c (md_enable): Do not allow combination of HMAC and
'expandable-output function'.
(md_final): Check if spec->read is NULL before calling.
(md_read): Ditto.
(md_extract, _gcry_md_extract): New.
* doc/gcrypt.texi: Add SHA3 algorithms and gcry_md_extract.
* src/cipher-proto.h (gcry_md_extract_t): New.
(gcry_md_spec_t): Add 'extract'.
* src/gcrypt-int.g (_gcry_md_extract): New.
* src/gcrypt.h.in (gcry_md_extract): New.
* src/libgcrypt.def: Add gcry_md_extract.
* src/libgcrypt.vers: Add gcry_md_extract.
* src/visibility.c (gcry_md_extract): New.
* src/visibility.h (gcry_md_extract): New.
--

Patch adds new interface for reading output from 'expandable-output
function' MD algorithms that can give variable length output (ie.
SHAKE algorithms from FIPS-202). New function to read output is

 gpg_error_t gcry_md_extract(gcry_md_hd_t md, int algo,
			     void *buffer, size_t length);

Function implicitly finalizes algorithm so that no new input can
be given. Subsequents calls of the function return more output
bytes from the algorithm.

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

1 files changed, 65 insertions, 2 deletions

diff --git a/cipher/md.c b/cipher/md.c
index 948d269b..6ef8fee9 100644
--- a/cipher/md.c
+++ b/cipher/md.c
@@ -408,6 +408,12 @@ md_enable (gcry_md_hd_t hd, int algorithm)
         }
     }
 
+  if (!err && h->flags.hmac && spec->read == NULL)
+    {
+      /* Expandable output function cannot act as part of HMAC. */
+      err = GPG_ERR_DIGEST_ALGO;
+    }
+
   if (!err)
     {
       size_t size = (sizeof (*entry)
@@ -638,11 +644,16 @@ md_final (gcry_md_hd_t a)
 
   for (r = a->ctx->list; r; r = r->next)
     {
-      byte *p = r->spec->read (&r->context.c);
+      byte *p;
       size_t dlen = r->spec->mdlen;
       byte *hash;
       gcry_err_code_t err;
 
+      if (r->spec->read == NULL)
+        continue;
+
+      p = r->spec->read (&r->context.c);
+
       if (a->ctx->flags.secure)
         hash = xtrymalloc_secure (dlen);
       else
@@ -821,6 +832,8 @@ md_read( gcry_md_hd_t a, int algo )
         {
           if (r->next)
             log_debug ("more than one algorithm in md_read(0)\n");
+          if (r->spec->read == NULL)
+            return NULL;
           return r->spec->read (&r->context.c);
         }
     }
@@ -828,7 +841,11 @@ md_read( gcry_md_hd_t a, int algo )
     {
       for (r = a->ctx->list; r; r = r->next)
 	if (r->spec->algo == algo)
-	  return r->spec->read (&r->context.c);
+	  {
+	    if (r->spec->read == NULL)
+	      return NULL;
+	    return r->spec->read (&r->context.c);
+	  }
     }
   BUG();
   return NULL;
@@ -850,6 +867,52 @@ _gcry_md_read (gcry_md_hd_t hd, int algo)
 }
 
 
+/****************
+ * If ALGO is null get the digest for the used algo (which should be
+ * only one)
+ */
+static gcry_err_code_t
+md_extract(gcry_md_hd_t a, int algo, void *out, size_t outlen)
+{
+  GcryDigestEntry *r = a->ctx->list;
+
+  if (!algo)
+    {
+      /* Return the first algorithm */
+      if (r && r->spec->extract)
+	{
+	  if (r->next)
+	    log_debug ("more than one algorithm in md_extract(0)\n");
+	  r->spec->extract (&r->context.c, out, outlen);
+	  return 0;
+	}
+    }
+  else
+    {
+      for (r = a->ctx->list; r; r = r->next)
+	if (r->spec->algo == algo && r->spec->extract)
+	  {
+	    r->spec->extract (&r->context.c, out, outlen);
+	    return 0;
+	  }
+    }
+
+  return GPG_ERR_DIGEST_ALGO;
+}
+
+
+/*
+ * Expand the output from XOF class digest, this function implictly finalizes
+ * the hash.
+ */
+gcry_err_code_t
+_gcry_md_extract (gcry_md_hd_t hd, int algo, void *out, size_t outlen)
+{
+  _gcry_md_ctl (hd, GCRYCTL_FINALIZE, NULL, 0);
+  return md_extract (hd, algo, out, outlen);
+}
+
+
 /*
  * Read out an intermediate digest.  Not yet functional.
  */