1 files changed, 85 insertions, 0 deletions
diff --git a/lib/libmpa/mpa_expmod.c b/lib/libmpa/mpa_expmod.c
new file mode 100644
index 0000000..d02c784
--- /dev/null
+++ b/lib/libmpa/mpa_expmod.c
@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2014, STMicroelectronics International N.V.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+#include "mpa.h"
+
+/*------------------------------------------------------------
+ *
+ *  mpa_exp_mod
+ *
+ *  Calculates dest = op1 ^ op2 mod n
+ *
+ */
+void mpa_exp_mod(mpanum dest,
+		const mpanum op1,
+		const mpanum op2,
+		const mpanum n,
+		const mpanum r_modn,
+		const mpanum r2_modn,
+		const mpa_word_t n_inv, mpa_scratch_mem pool)
+{
+	mpanum A;
+	mpanum B;
+	mpanum xtilde;
+	mpanum *ptr_a;
+	mpanum *ptr_b;
+	mpanum *swapper;
+	int idx;
+
+	mpa_alloc_static_temp_var(&A, pool);
+	mpa_alloc_static_temp_var(&B, pool);
+	mpa_alloc_static_temp_var(&xtilde, pool);
+
+	/* transform to Montgomery space */
+	/* use internal version since xtidle is big enough */
+	__mpa_montgomery_mul(xtilde, op1, r2_modn, n, n_inv);
+
+	mpa_copy(A, r_modn);
+	ptr_a = &A;
+	ptr_b = &B;
+	__mpa_set_unused_digits_to_zero(A);
+	__mpa_set_unused_digits_to_zero(B);
+	for (idx = mpa_highest_bit_index(op2); idx >= 0; idx--) {
+		__mpa_montgomery_mul(*ptr_b, *ptr_a, *ptr_a, n, n_inv);
+		if (mpa_get_bit(op2, idx) == 1) {
+			__mpa_montgomery_mul(*ptr_a, *ptr_b, xtilde, n, n_inv);
+		} else {
+			swapper = ptr_a;
+			ptr_a = ptr_b;
+			ptr_b = swapper;
+		}
+	}
+
+	/* transform back form Montgomery space */
+	__mpa_montgomery_mul(*ptr_b, (const mpanum)&const_one, *ptr_a,
+			     n, n_inv);
+
+	mpa_copy(dest, *ptr_b);
+
+	mpa_free_static_temp_var(&A, pool);
+	mpa_free_static_temp_var(&B, pool);
+	mpa_free_static_temp_var(&xtilde, pool);
+}