--- /dev/null
+From 707c3c5c511ee70ad0e39ec613471f665305fbea Mon Sep 17 00:00:00 2001
+From: NIIBE Yutaka <gniibe@fsij.org>
+Date: Fri, 21 May 2021 11:15:07 +0900
+Subject: [PATCH] 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>
+
+Upstream-Status: Backport
+CVE: CVE-2021-33560
+Signed-off-by: Armin Kuster <akuster@mvista.com>
+---
+ cipher/elgamal.c | 24 ++++++------------------
+ 1 file changed, 6 insertions(+), 18 deletions(-)
+
+diff --git a/cipher/elgamal.c b/cipher/elgamal.c
+index 4eb52d62..ae7a631e 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
+@@ -594,7 +582,7 @@ 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 );
+--
+2.30.2
+
