symm/gaead.h: Introduce a new abstraction for authenticated encryption.

[catacomb] / symm / gaead.c

diff --git a/symm/gaead.c b/symm/gaead.c
new file mode 100644 (file)
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+++ b/symm/gaead.c
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+/* -*-c-*-
+ *
+ * Generic authenticated encryption interface
+ *
+ * (c) 2018 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------*
+ *
+ * This file is part of Catacomb.
+ *
+ * Catacomb is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Library General Public License as published
+ * by the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * Catacomb 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
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with Catacomb.  If not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+ * USA.
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include "gaead.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @gaead_encrypt@ --- *
+ *
+ * Arguments:  @const gaead_key *k@ = the AEAD key, already prepared
+ *             @const void *n@, @size_t nsz@ = nonce
+ *             @const void *h@, @size_t hsz@ = additional `header' data
+ *             @const void *m@, @size_t msz@ = message input
+ *             @void *c@, @size_t *csz_input@ = ciphertext output
+ *             @void *t@, @size_t tsz@ = tag output
+ *
+ * Returns:    Zero on success, @-1@ if the output buffer is too small.
+ *
+ * Use:                Encrypts and authenticates a message in a single operation.
+ *             This just saves a bunch of messing about with the various
+ *             @gaead_...@ objects.
+ *
+ *             On entry, @*csz_inout@ should be the capacity of the
+ *             ciphertext buffer; on exit, it will be updated with the
+ *             actual size of ciphertext produced.  The function will not
+ *             fail if @*csz_inout >= msz + k->c->ohd@.
+ */
+
+int gaead_encrypt(const gaead_key *k, const void *n, size_t nsz,
+                 const void *h, size_t hsz,
+                 const void *m, size_t msz,
+                 void *c, size_t *csz_inout,
+                 void *t, size_t tsz)
+{
+  gaead_enc *e = 0;
+  gaead_aad *a = 0;
+  buf b;
+  int rc;
+
+  buf_init(&b, c, *csz_inout);
+  e = GAEAD_ENC(k, n, nsz, hsz, msz, tsz); if (!e) { rc = -1; goto end; }
+  if (hsz) { a = GAEAD_AAD(e); GAEAD_HASH(a, h, hsz); }
+  rc = GAEAD_ENCRYPT(e, m, msz, &b); if (rc) goto end;
+  rc = GAEAD_DONE(e, a, &b, t, tsz);
+end:
+  if (rc >= 0) *csz_inout = BLEN(&b);
+  if (e) GAEAD_DESTROY(e);
+  if (a) GAEAD_DESTROY(a);
+  return (rc);
+}
+
+/* --- @gaead_decrypt@ --- *
+ *
+ * Arguments:  @const gaead_key *k@ = the AEAD key, already prepared
+ *             @const void *n@, @size_t nsz@ = nonce
+ *             @const void *h@, @size_t hsz@ = additional `header' data
+ *             @const void *c@, @size_t csz@ = ciphertext input
+ *             @void *m@, @size_t *msz_inout@ = message output
+ *             @const void *t@, @size_t tsz@ = tag input
+ *
+ * Returns:    @+1@ if everything is good; zero for authentication failure,
+ *             @-1@ for other problems.
+ *
+ * Use:                Decrypts and verifies a message in a single operation.
+ *             This just saves a bunch of messing about with the various
+ *             @gaead_...@ objects.
+ *
+ *             On entry, @*msz_inout@ should be the capacity of the
+ *             message buffer; on exit, it will be updated with the
+ *             actual size of message produced.  The function will not
+ *             fail if @*msz_inout >= csz@.
+ */
+
+int gaead_decrypt(const gaead_key *k, const void *n, size_t nsz,
+                 const void *h, size_t hsz,
+                 const void *c, size_t csz,
+                 void *m, size_t *msz_inout,
+                 const void *t, size_t tsz)
+{
+  gaead_dec *d = 0;
+  gaead_aad *a = 0;
+  buf b;
+  int rc;
+
+  buf_init(&b, m, *msz_inout);
+  d = GAEAD_DEC(k, n, nsz, hsz, csz, tsz); if (!d) { rc = -1; goto end; }
+  if (hsz) { a = GAEAD_AAD(d); GAEAD_HASH(a, h, hsz); }
+  rc = GAEAD_DECRYPT(d, c, csz, &b); if (rc) goto end;
+  rc = GAEAD_DONE(d, a, &b, t, tsz);
+end:
+  if (rc >= 0) *msz_inout = BLEN(&b);
+  if (d) GAEAD_DESTROY(d);
+  if (a) GAEAD_DESTROY(a);
+  return (rc);
+}
+
+/*----- That's all, folks -------------------------------------------------*/