Add FFC param/key generation

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10909)

1 files changed, 61 insertions, 0 deletions

diff --git a/crypto/ffc/ffc_key_generate.c b/crypto/ffc/ffc_key_generate.c
new file mode 100644
index 0000000000..186245cc87
--- /dev/null
+++ b/crypto/ffc/ffc_key_generate.c
@@ -0,0 +1,61 @@
+/*
+ * Copyright 2019-2020 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#include "internal/ffc.h"
+
+/*
+ * SP800-56Ar3 5.6.1.1.4 Key pair generation by testing candidates.
+ * Generates a private key in the interval [1, min(2 ^ N - 1, q - 1)].
+ *
+ * ctx must be set up with a libctx (for fips mode).
+ * params contains the FFC domain parameters p, q and g (for DH or DSA).
+ * N is the maximum bit length of the generated private key,
+ * s is the security strength.
+ * priv_key is the returned private key,
+ */
+int ffc_generate_private_key(BN_CTX *ctx, const FFC_PARAMS *params,
+                             int N, int s, BIGNUM *priv)
+{
+#ifdef FIPS_MODE
+    int ret = 0;
+    BIGNUM *m, *two_powN = NULL;
+
+    /* Step (2) : check range of N */
+    if (N < 2 * s || N > BN_num_bits(params->q))
+        return 0;
+
+    two_powN = BN_new();
+    /* 2^N */
+    if (two_powN == NULL || !BN_lshift(two_powN, BN_value_one(), N))
+        goto err;
+
+    /* Step (5) : M = min(2 ^ N, q) */
+    m = (BN_cmp(two_powN, params->q) > 0) ? params->q : two_powN;
+    do {
+        /* Steps (3, 4 & 7) :  c + 1 = 1 + random[0..2^N - 1] */
+        if (!BN_priv_rand_range_ex(priv, two_powN, ctx)
+            || !BN_add_word(priv, 1))
+            goto err;
+        /* Step (6) : loop if c > M - 2 (i.e. c + 1 >= M) */
+        if (BN_cmp(priv, m) < 0)
+            break;
+    } while (1);
+
+    ret = 1;
+err:
+    BN_free(two_powN);
+    return ret;
+#else
+    do {
+        if (!BN_priv_rand_range_ex(priv, params->q, ctx))
+            return 0;
+    } while (BN_is_zero(priv) || BN_is_one(priv));
+    return 1;
+#endif /* FIPS_MODE */
+}