1 files changed, 133 insertions, 0 deletions
diff --git a/lib/mpi/mpi-mpow.c b/lib/mpi/mpi-mpow.c
new file mode 100644
index 000000000000..4cc75933c5a7
--- /dev/null
+++ b/lib/mpi/mpi-mpow.c
@@ -0,0 +1,133 @@
+/* mpi-mpow.c  -  MPI functions
+ * Copyright (C) 1998, 1999, 2000 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"
+#include "longlong.h"
+
+static int build_index(const MPI *exparray, int k, int i, int t)
+{
+	int j, bitno;
+	int index = 0;
+
+	bitno = t - i;
+	for (j = k - 1; j >= 0; j--) {
+		index <<= 1;
+		if (mpi_test_bit(exparray[j], bitno))
+			index |= 1;
+	}
+	return index;
+}
+
+/****************
+ * RES = (BASE[0] ^ EXP[0]) *  (BASE[1] ^ EXP[1]) * ... * mod M
+ */
+int mpi_mulpowm(MPI res, MPI *basearray, MPI *exparray, MPI m)
+{
+	int rc = -ENOMEM;
+	int k;			/* number of elements */
+	int t;			/* bit size of largest exponent */
+	int i, j, idx;
+	MPI *G = NULL;		/* table with precomputed values of size 2^k */
+	MPI tmp = NULL;
+
+	for (k = 0; basearray[k]; k++)
+		;
+	if (!k) {
+		pr_emerg("mpi_mulpowm: assert(k) failed\n");
+		BUG();
+	}
+	for (t = 0, i = 0; (tmp = exparray[i]); i++) {
+		j = mpi_get_nbits(tmp);
+		if (j > t)
+			t = j;
+	}
+	if (i != k) {
+		pr_emerg("mpi_mulpowm: assert(i==k) failed\n");
+		BUG();
+	}
+	if (!t) {
+		pr_emerg("mpi_mulpowm: assert(t) failed\n");
+		BUG();
+	}
+	if (k >= 10) {
+		pr_emerg("mpi_mulpowm: assert(k<10) failed\n");
+		BUG();
+	}
+
+	G = kzalloc((1 << k) * sizeof *G, GFP_KERNEL);
+	if (!G)
+		goto nomem;
+
+	/* and calculate */
+	tmp = mpi_alloc(mpi_get_nlimbs(m) + 1);
+	if (!tmp)
+		goto nomem;
+	if (mpi_set_ui(res, 1) < 0)
+		goto nomem;
+	for (i = 1; i <= t; i++) {
+		if (mpi_mulm(tmp, res, res, m) < 0)
+			goto nomem;
+		idx = build_index(exparray, k, i, t);
+		if (!(idx >= 0 && idx < (1 << k))) {
+			pr_emerg("mpi_mulpowm: assert(idx >= 0 && idx < (1<<k)) failed\n");
+			BUG();
+		}
+		if (!G[idx]) {
+			if (!idx) {
+				G[0] = mpi_alloc_set_ui(1);
+				if (!G[0])
+					goto nomem;
+			} else {
+				for (j = 0; j < k; j++) {
+					if ((idx & (1 << j))) {
+						if (!G[idx]) {
+							if (mpi_copy
+							    (&G[idx],
+							     basearray[j]) < 0)
+								goto nomem;
+						} else {
+							if (mpi_mulm
+							    (G[idx], G[idx],
+							     basearray[j],
+							     m) < 0)
+								goto nomem;
+						}
+					}
+				}
+				if (!G[idx]) {
+					G[idx] = mpi_alloc(0);
+					if (!G[idx])
+						goto nomem;
+				}
+			}
+		}
+		if (mpi_mulm(res, tmp, G[idx], m) < 0)
+			goto nomem;
+	}
+
+	rc = 0;
+nomem:
+	/* cleanup */
+	mpi_free(tmp);
+	for (i = 0; i < (1 << k); i++)
+		mpi_free(G[i]);
+	kfree(G);
+	return rc;
+}