1 files changed, 114 insertions, 0 deletions

diff --git a/src/lib/libcrypto/bn/bn_mod_words.c b/src/lib/libcrypto/bn/bn_mod_words.c
new file mode 100644
index 0000000000..d9aee8701a
--- /dev/null
+++ b/src/lib/libcrypto/bn/bn_mod_words.c
@@ -0,0 +1,114 @@
+/*      $OpenBSD: bn_mod_words.c,v 1.3 2025/08/05 15:15:54 jsing Exp $  */
+/*
+ * Copyright (c) 2024 Joel Sing <jsing@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "bn_local.h"
+#include "bn_internal.h"
+
+/*
+ * bn_mod_add_words() computes r[] = (a[] + b[]) mod m[], where a, b, r and
+ * m are arrays of words with length n (r may be the same as a or b).
+ */
+#ifndef HAVE_BN_MOD_ADD_WORDS
+void
+bn_mod_add_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
+    const BN_ULONG *m, size_t n)
+{
+        BN_ULONG carry, mask;
+
+        /*
+         * Compute a + b, then compute r - m to determine if r >= m, considering
+         * any carry that resulted from the addition. Finally complete a
+         * conditional subtraction of r - m.
+         */
+        /* XXX - change bn_add_words to use size_t. */
+        carry = bn_add_words(r, a, b, n);
+        mask = ~(carry - bn_sub_words_borrow(r, m, n));
+        bn_sub_words_masked(r, r, m, mask, n);
+}
+#endif
+
+/*
+ * bn_mod_sub_words() computes r[] = (a[] - b[]) mod m[], where a, b, r and
+ * m are arrays of words with length n (r may be the same as a or b).
+ */
+#ifndef HAVE_BN_MOD_SUB_WORDS
+void
+bn_mod_sub_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
+    const BN_ULONG *m, size_t n)
+{
+        BN_ULONG borrow, mask;
+
+        /*
+         * Compute a - b, then complete a conditional addition of r + m
+         * based on the resulting borrow.
+         */
+        /* XXX - change bn_sub_words to use size_t. */
+        borrow = bn_sub_words(r, a, b, n);
+        mask = (0 - borrow);
+        bn_add_words_masked(r, r, m, mask, n);
+}
+#endif
+
+/*
+ * bn_mod_mul_words() computes r[] = (a[] * b[]) mod m[], where a, b, r and
+ * m are arrays of words with length n (r may be the same as a or b) in the
+ * Montgomery domain. The result remains in the Montgomery domain.
+ */
+#ifndef HAVE_BN_MOD_MUL_WORDS
+void
+bn_mod_mul_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
+    const BN_ULONG *m, BN_ULONG *t, BN_ULONG m0, size_t n)
+{
+        if (n == 4) {
+                bn_mul_comba4(t, a, b);
+                bn_montgomery_reduce_words(r, t, m, m0, n);
+        } else if (n == 6) {
+                bn_mul_comba6(t, a, b);
+                bn_montgomery_reduce_words(r, t, m, m0, n);
+        } else if (n == 8) {
+                bn_mul_comba8(t, a, b);
+                bn_montgomery_reduce_words(r, t, m, m0, n);
+        } else {
+                bn_montgomery_multiply_words(r, a, b, m, t, m0, n);
+        }
+}
+#endif
+
+/*
+ * bn_mod_sqr_words() computes r[] = (a[] * a[]) mod m[], where a, r and
+ * m are arrays of words with length n (r may be the same as a) in the
+ * Montgomery domain. The result remains in the Montgomery domain.
+ */
+#ifndef HAVE_BN_MOD_SQR_WORDS
+void
+bn_mod_sqr_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *m,
+    BN_ULONG *t, BN_ULONG m0, size_t n)
+{
+        if (n == 4) {
+                bn_sqr_comba4(t, a);
+                bn_montgomery_reduce_words(r, t, m, m0, n);
+        } else if (n == 6) {
+                bn_sqr_comba6(t, a);
+                bn_montgomery_reduce_words(r, t, m, m0, n);
+        } else if (n == 8) {
+                bn_sqr_comba8(t, a);
+                bn_montgomery_reduce_words(r, t, m, m0, n);
+        } else {
+                bn_montgomery_multiply_words(r, a, a, m, t, m0, n);
+        }
+}
+#endif