commit b2967960e594d9e2c84edc5fe331bba531e0def5
Author: Ian Goldberg <iang@cs.uwaterloo.ca>
Date:   Wed Jul 17 09:30:52 2013 -0400

    Workaround for a crash bug in libgcrypt affecting otr_sesskeys
    
    Passing a private key value of 0 to otr_sesskeys would cause libgcrypt
    to crash in gcry_mpi_powm.  We reported this libgcrypt bug and it was
    then fixed in
    http://lists.gnupg.org/pipermail/gcrypt-devel/2013-July/002251.html
    but the workaround is simply to use gcry_mpi_new(DH1536_MOD_LEN_BITS)
    instead of gcry_mpi_new(0).
    
    Note that this only affected the otr_sesskeys toolkit program, and not
    libotr itself.
    
    Thanks to the Mayhem Team at CMU (Alexandre Rebert, Thanassis Avgerinos,
    Sang Kil Cha, David Brumley, Manuel Egele) for the report.

diff --git a/toolkit/sesskeys.c b/toolkit/sesskeys.c
index 575e984..d416cde 100644
--- a/toolkit/sesskeys.c
+++ b/toolkit/sesskeys.c
@@ -32,6 +32,7 @@ static const char* DH1536_MODULUS_S = "0x"
     "C2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F"
     "83655D23DCA3AD961C62F356208552BB9ED529077096966D"
     "670C354E4ABC9804F1746C08CA237327FFFFFFFFFFFFFFFF";
+static const int DH1536_MOD_LEN_BITS = 1536;
 static const char *DH1536_GENERATOR_S = "0x02";
 
 /* Generate the session id and the two encryption keys from our private
@@ -52,9 +53,9 @@ void sesskeys_gen(unsigned char sessionid[20], unsigned char sendenc[16],
 	(const unsigned char *)DH1536_MODULUS_S, 0, NULL);
     gcry_mpi_scan(&generator, GCRYMPI_FMT_HEX,
 	(const unsigned char *)DH1536_GENERATOR_S, 0, NULL);
-    *our_yp = gcry_mpi_new(0);
+    *our_yp = gcry_mpi_new(DH1536_MOD_LEN_BITS);
     gcry_mpi_powm(*our_yp, generator, our_x, modulus);
-    secretv = gcry_mpi_new(0);
+    secretv = gcry_mpi_new(DH1536_MOD_LEN_BITS);
     gcry_mpi_powm(secretv, their_y, our_x, modulus);
     gcry_mpi_release(generator);
     gcry_mpi_release(modulus);