libgcrypt: make it compatible with chacha20

Signed-off-by: Aris Adamantiadis <aris@0xbadc0de.be>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/libgcrypt.h

@@ -88,6 +88,7 @@ ssh_string ssh_sexp_extract_mpi(const gcry_sexp_t sexp,
 
 #endif /* HAVE_LIBGCRYPT */
 
+void libgcrypt_init(void);
 struct ssh_cipher_struct *ssh_get_ciphertab(void);
 
 #endif /* LIBGCRYPT_H_ */

src/dh.c

@@ -190,6 +190,7 @@ int ssh_crypto_init(void) {
       p_group1 = NULL;
       return -1;
     }
+    libgcrypt_init();
 
 #elif defined HAVE_LIBCRYPTO
     p_group1 = bignum_new();

src/libgcrypt.c

@@ -35,6 +35,8 @@
 #ifdef HAVE_LIBGCRYPT
 #include <gcrypt.h>
 
+extern const struct ssh_cipher_struct chacha20poly1305_cipher;
+
 struct ssh_mac_ctx_struct {
   enum ssh_mac_e mac_type;
   gcry_md_hd_t ctx;
@@ -637,6 +639,9 @@ static struct ssh_cipher_struct ssh_ciphertab[] = {
     .encrypt     = des1_1_encrypt,
     .decrypt     = des1_1_decrypt
   },
+  {
+    .name = "chacha20-poly1305@openssh.com"
+  },
   {
     .name            = NULL,
     .blocksize       = 0,
@@ -650,6 +655,22 @@ static struct ssh_cipher_struct ssh_ciphertab[] = {
   }
 };
 
+void libgcrypt_init(void)
+{
+    size_t i;
+
+    for (i = 0; ssh_ciphertab[i].name != NULL; i++) {
+        int cmp;
+        cmp = strcmp(ssh_ciphertab[i].name, "chacha20-poly1305@openssh.com");
+        if (cmp == 0) {
+            memcpy(&ssh_ciphertab[i],
+                   &chacha20poly1305_cipher,
+                   sizeof(struct ssh_cipher_struct));
+            break;
+        }
+    }
+}
+
 struct ssh_cipher_struct *ssh_get_ciphertab(void)
 {
   return ssh_ciphertab;