Fix for CVE-2021-33560

Resolves: rhbz#1971422

libgcrypt-1.9.3-CVE-2021-33560.patch

@@ -0,0 +1,100 @@
+commit 3462280f2e23e16adf3ed5176e0f2413d8861320
+Author: NIIBE Yutaka <gniibe@fsij.org>
+Date:   Fri May 21 11:15:07 2021 +0900
+
+    cipher: Fix ElGamal encryption for other implementations.
+    
+    * cipher/elgamal.c (gen_k): Remove support of smaller K.
+    (do_encrypt): Never use smaller K.
+    (sign): Folllow the change of gen_k.
+    
+    --
+    
+    Cherry-pick master commit of:
+            632d80ef30e13de6926d503aa697f92b5dbfbc5e
+    
+    This change basically reverts encryption changes in two commits:
+    
+            74386120dad6b3da62db37f7044267c8ef34689b
+            78531373a342aeb847950f404343a05e36022065
+    
+    Use of smaller K for ephemeral key in ElGamal encryption is only good,
+    when we can guarantee that recipient's key is generated by our
+    implementation (or compatible).
+    
+    For detail, please see:
+    
+        Luca De Feo, Bertram Poettering, Alessandro Sorniotti,
+        "On the (in)security of ElGamal in OpenPGP";
+        in the proceedings of  CCS'2021.
+    
+    CVE-id: CVE-2021-33560
+    GnuPG-bug-id: 5328
+    Suggested-by: Luca De Feo, Bertram Poettering, Alessandro Sorniotti
+    Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
+
+diff --git a/cipher/elgamal.c b/cipher/elgamal.c
+index 9835122f..eead4502 100644
+--- a/cipher/elgamal.c
++++ b/cipher/elgamal.c
+@@ -66,7 +66,7 @@ static const char *elg_names[] =
+ 
+ 
+ static int test_keys (ELG_secret_key *sk, unsigned int nbits, int nodie);
+-static gcry_mpi_t gen_k (gcry_mpi_t p, int small_k);
++static gcry_mpi_t gen_k (gcry_mpi_t p);
+ static gcry_err_code_t generate (ELG_secret_key *sk, unsigned nbits,
+                                  gcry_mpi_t **factors);
+ static int  check_secret_key (ELG_secret_key *sk);
+@@ -189,11 +189,10 @@ test_keys ( ELG_secret_key *sk, unsigned int nbits, int nodie )
+ 
+ /****************
+  * Generate a random secret exponent k from prime p, so that k is
+- * relatively prime to p-1.  With SMALL_K set, k will be selected for
+- * better encryption performance - this must never be used signing!
++ * relatively prime to p-1.
+  */
+ static gcry_mpi_t
+-gen_k( gcry_mpi_t p, int small_k )
++gen_k( gcry_mpi_t p )
+ {
+   gcry_mpi_t k = mpi_alloc_secure( 0 );
+   gcry_mpi_t temp = mpi_alloc( mpi_get_nlimbs(p) );
+@@ -202,18 +201,7 @@ gen_k( gcry_mpi_t p, int small_k )
+   unsigned int nbits, nbytes;
+   char *rndbuf = NULL;
+ 
+-  if (small_k)
+-    {
+-      /* Using a k much lesser than p is sufficient for encryption and
+-       * it greatly improves the encryption performance.  We use
+-       * Wiener's table and add a large safety margin. */
+-      nbits = wiener_map( orig_nbits ) * 3 / 2;
+-      if( nbits >= orig_nbits )
+-        BUG();
+-    }
+-  else
+-    nbits = orig_nbits;
+-
++  nbits = orig_nbits;
+ 
+   nbytes = (nbits+7)/8;
+   if( DBG_CIPHER )
+@@ -492,7 +480,7 @@ do_encrypt(gcry_mpi_t a, gcry_mpi_t b, gcry_mpi_t input, ELG_public_key *pkey )
+    * error code.
+    */
+ 
+-  k = gen_k( pkey->p, 1 );
++  k = gen_k( pkey->p );
+   mpi_powm (a, pkey->g, k, pkey->p);
+ 
+   /* b = (y^k * input) mod p
+@@ -608,7 +596,7 @@ sign(gcry_mpi_t a, gcry_mpi_t b, gcry_mpi_t input, ELG_secret_key *skey )
+     *
+     */
+     mpi_sub_ui(p_1, p_1, 1);
+-    k = gen_k( skey->p, 0 /* no small K ! */ );
++    k = gen_k( skey->p );
+     mpi_powm( a, skey->g, k, skey->p );
+     mpi_mul(t, skey->x, a );
+     mpi_subm(t, input, t, p_1 );

libgcrypt.spec

@@ -48,6 +48,8 @@ Patch27: libgcrypt-1.8.3-md-fips-enforce.patch
 Patch28: libgcrypt-1.8.5-intel-cet.patch
 # FIPS module is redefined a little bit (implicit by kernel FIPS mode)
 Patch30: libgcrypt-1.8.5-fips-module.patch
+# Fix for CVE-2021-33560
+Patch31: libgcrypt-1.9.3-CVE-2021-33560.patch
 
 %global gcrylibdir %{_libdir}
 %global gcrysoname libgcrypt.so.20
@@ -97,6 +99,7 @@ applications using libgcrypt.
 %patch27 -p1 -b .fips-enforce
 %patch28 -p1 -b .intel-cet
 %patch30 -p1 -b .fips-module
+%patch31 -p1 -b .CVE-2021-33560
 
 cp %{SOURCE4} cipher/
 cp %{SOURCE5} %{SOURCE6} %{SOURCE8} tests/