diff --git a/lib/mpi/mpi-gcd.c b/lib/mpi/mpi-gcd.c
new file mode 100644
index 0000000..13c48ae
--- /dev/null
+++ b/lib/mpi/mpi-gcd.c
@@ -0,0 +1,59 @@
+/* mpi-gcd.c  -  MPI functions
+ * Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+#include "mpi-internal.h"
+
+/****************
+ * Find the greatest common divisor G of A and B.
+ * Return: true if this 1, false in all other cases
+ */
+int mpi_gcd(MPI g, const MPI xa, const MPI xb)
+{
+	MPI a = NULL, b = NULL;
+
+	if (mpi_copy(&a, xa) < 0)
+		goto nomem;
+
+	if (mpi_copy(&b, xb) < 0)
+		goto nomem;
+
+	/* TAOCP Vol II, 4.5.2, Algorithm A */
+	a->sign = 0;
+	b->sign = 0;
+	while (mpi_cmp_ui(b, 0)) {
+		if (mpi_fdiv_r(g, a, b) < 0)	/* g used as temorary variable */
+			goto nomem;
+		if (mpi_set(a, b) < 0)
+			goto nomem;
+		if (mpi_set(b, g) < 0)
+			goto nomem;
+	}
+	if (mpi_set(g, a) < 0)
+		goto nomem;
+
+	mpi_free(a);
+	mpi_free(b);
+	return !mpi_cmp_ui(g, 1);
+
+nomem:
+	mpi_free(a);
+	mpi_free(b);
+	return -ENOMEM;
+}