gpg: Support ECDH with v5 key.

* g10/ecdh.c (build_kdf_params): Use the first 20 octets.
* g10/pkglue.c (pk_encrypt): Remove length check to 20.
* g10/pubkey-enc.c (get_it): Likewise.

Signed-off-by: NIIBE Yutaka <[email protected]>

3 files changed, 10 insertions, 10 deletions

diff --git a/g10/ecdh.c b/g10/ecdh.c
index ac2883cf4..9a1f535a0 100644
--- a/g10/ecdh.c
+++ b/g10/ecdh.c
@@ -129,6 +129,13 @@ extract_secret_x (byte **r_secret_x,
 }
 
 
+/* Build KDF parameters */
+/* RFC 6637 defines the KDF parameters and its encoding in Section
+   8. EC DH Algorighm (ECDH).  Since it was written for v4 key, it
+   said "20 octets representing a recipient encryption subkey or a
+   master key fingerprint".  For v5 key, it is considered "adequate"
+   (in terms of NIST SP 800 56A, see 5.8.2 FixedInfo) to use the first
+   20 octets of its 32 octets fingerprint.  */
 static gpg_error_t
 build_kdf_params (unsigned char kdf_params[256], size_t *r_size,
                   gcry_mpi_t *pkey, const byte pk_fp[MAX_FINGERPRINT_LEN])
@@ -150,7 +157,7 @@ build_kdf_params (unsigned char kdf_params[256], size_t *r_size,
   err = (err ? err : gpg_mpi_write_nohdr (obuf, pkey[2]));
   /* fixed-length field 4 */
   iobuf_write (obuf, "Anonymous Sender    ", 20);
-  /* fixed-length field 5, recipient fp */
+  /* fixed-length field 5, recipient fp (or first 20 octets of fp) */
   iobuf_write (obuf, pk_fp, 20);
 
   if (!err)
diff --git a/g10/pkglue.c b/g10/pkglue.c
index 13f8e2f03..cab007f01 100644
--- a/g10/pkglue.c
+++ b/g10/pkglue.c
@@ -419,7 +419,6 @@ pk_encrypt (pubkey_algo_t algo, gcry_mpi_t *resarr, gcry_mpi_t data,
     {
       gcry_mpi_t public, result;
       byte fp[MAX_FINGERPRINT_LEN];
-      size_t fpn;
       byte *shared;
       size_t nshared;
 
@@ -436,9 +435,7 @@ pk_encrypt (pubkey_algo_t algo, gcry_mpi_t *resarr, gcry_mpi_t data,
         }
 
       result = NULL;
-      fingerprint_from_pk (pk, fp, &fpn);
-      if (fpn != 20)
-        rc = gpg_error (GPG_ERR_INV_LENGTH);
+      fingerprint_from_pk (pk, fp, NULL);
 
       if (!rc)
         {
diff --git a/g10/pubkey-enc.c b/g10/pubkey-enc.c
index 9a2c107f8..6e1b0898e 100644
--- a/g10/pubkey-enc.c
+++ b/g10/pubkey-enc.c
@@ -201,7 +201,6 @@ get_it (ctrl_t ctrl,
   char *desc;
   char *keygrip;
   byte fp[MAX_FINGERPRINT_LEN];
-  size_t fpn;
 
   if (DBG_CLOCK)
     log_clock ("decryption start");
@@ -245,10 +244,7 @@ get_it (ctrl_t ctrl,
     goto leave;
 
   if (sk->pubkey_algo == PUBKEY_ALGO_ECDH)
-    {
-      fingerprint_from_pk (sk, fp, &fpn);
-      log_assert (fpn == 20);
-    }
+    fingerprint_from_pk (sk, fp, NULL);
 
   /* Decrypt. */
   desc = gpg_format_keydesc (ctrl, sk, FORMAT_KEYDESC_NORMAL, 1);