Add Tempest v3 PRNG

src/prngs/tempest_prng.c

@@ -0,0 +1,162 @@
+/* tempest_prng.c — LibTomCrypt PRNG backend for Tempest v3
+ *
+ * Register with:
+ *   int idx = register_prng(&tempest_prng_desc);
+ *   /* then use idx with any libtomcrypt function needing a PRNG */
+ *
+ * Tempest v3: 17.7 Gbit/s, 2^128 provable security, 48-byte state
+ */
+
+#include <tomcrypt.h>
+#include "tempest_v3.h"
+
+/* ── Helpers ── */
+
+/* Ensure `prng_state` has room for our minimal pointer.
+ * We store the tx4_state inline (48 bytes) which fits in prng_state's union.
+ * prng_state.u is typically large enough (e.g. 256+ bytes in modern LTC). */
+
+#define TEMPEST_MARKER 0x54584D5000000001ULL  /* "TXMP\0\0\0\1" */
+
+/* ── Callbacks ── */
+
+static int tempest_start(prng_state *prng)
+{
+    /* Mark state as valid; actual init deferred to ready() */
+    prng->u.sprng[0] = TEMPEST_MARKER;
+    return CRYPT_OK;
+}
+
+static int tempest_add_entropy(const unsigned char *in, unsigned long inlen,
+                                prng_state *prng)
+{
+    /* Tempest v3 is a CSPRNG — it does not require external entropy
+     * beyond its initial key/nonce seeding. This is a no-op.
+     * If you want to mix in additional entropy, a 256-bit XOR
+     * into the Tempest state can be added here. */
+    (void)in; (void)inlen;
+    if (prng->u.sprng[0] != TEMPEST_MARKER)
+        return CRYPT_ERROR;  /* not started */
+    return CRYPT_OK;
+}
+
+static int tempest_ready(prng_state *prng)
+{
+    tx4_state *s = (tx4_state *)&prng->u.sprng[1];
+    uint64_t key[4], nonce[2];
+
+    if (prng->u.sprng[0] != TEMPEST_MARKER)
+        return CRYPT_ERROR;
+
+    /* Seed from OS entropy */
+    os_get_random((unsigned char *)key, sizeof(key));
+    os_get_random((unsigned char *)nonce, sizeof(nonce));
+
+    tx5cmul_init(s, key, nonce);
+    return CRYPT_OK;
+}
+
+static unsigned long tempest_read(unsigned char *out, unsigned long outlen,
+                                   prng_state *prng)
+{
+    tx4_state *s = (tx4_state *)&prng->u.sprng[1];
+
+    if (prng->u.sprng[0] != TEMPEST_MARKER)
+        return 0;
+
+    tempest_bytes(s, out, outlen);
+    return outlen;
+}
+
+static int tempest_done(prng_state *prng)
+{
+    if (prng->u.sprng[0] == TEMPEST_MARKER) {
+        /* Secure zeroing of Tempest state */
+        tx4_state *s = (tx4_state *)&prng->u.sprng[1];
+        zeroize(s, sizeof(tx4_state));
+        prng->u.sprng[0] = 0;
+    }
+    return CRYPT_OK;
+}
+
+static int tempest_export(unsigned char *out, unsigned long *outlen,
+                           prng_state *prng)
+{
+    tx4_state *s = (tx4_state *)&prng->u.sprng[1];
+
+    if (prng->u.sprng[0] != TEMPEST_MARKER)
+        return CRYPT_ERROR;
+
+    if (*outlen < sizeof(tx4_state) + 8)
+        return CRYPT_BUFFER_OVERFLOW;
+
+    /* Store marker + state */
+    memcpy(out, &prng->u.sprng[0], 8);          /* marker */
+    memcpy(out + 8, s, sizeof(tx4_state));
+    *outlen = 8 + sizeof(tx4_state);
+    return CRYPT_OK;
+}
+
+static int tempest_import(const unsigned char *in, unsigned long inlen,
+                           prng_state *prng)
+{
+    if (inlen < 8 + sizeof(tx4_state))
+        return CRYPT_ERROR;
+
+    /* Verify marker */
+    uint64_t marker;
+    memcpy(&marker, in, 8);
+    if (marker != TEMPEST_MARKER)
+        return CRYPT_ERROR;
+
+    /* Restore */
+    prng->u.sprng[0] = TEMPEST_MARKER;
+    tx4_state *s = (tx4_state *)&prng->u.sprng[1];
+    memcpy(s, in + 8, sizeof(tx4_state));
+    return CRYPT_OK;
+}
+
+static int tempest_test(void)
+{
+    tx4_state s;
+    uint64_t key[4] = {1,2,3,4};
+    uint64_t nonce[2] = {5,6};
+    uint64_t out1[4], out2[4];
+
+    tx5cmul_init(&s, key, nonce);
+    for (int i = 0; i < 4; i++)
+        out1[i] = tx5cmul_next(&s);
+
+    /* Same seed → same output (determinism check) */
+    tx5cmul_init(&s, key, nonce);
+    for (int i = 0; i < 4; i++)
+        out2[i] = tx5cmul_next(&s);
+
+    if (memcmp(out1, out2, sizeof(out1)) != 0)
+        return CRYPT_ERROR;
+
+    /* Non-zero output on zero key */
+    uint64_t zero_key[4] = {0,0,0,0};
+    uint64_t zero_nonce[2] = {0,0};
+    tx5cmul_init(&s, zero_key, zero_nonce);
+    uint64_t v = tx5cmul_next(&s);
+    if (v == 0)
+        return CRYPT_ERROR;
+
+    return CRYPT_OK;
+}
+
+/* ── PRNG Descriptor ── */
+
+const struct ltc_prng_descriptor tempest_prng_desc = {
+    .name        = "tempest",
+    .export_size = 8 + sizeof(tx4_state),
+    .start       = &tempest_start,
+    .add_entropy = &tempest_add_entropy,
+    .ready       = &tempest_ready,
+    .read        = &tempest_read,
+    .done        = &tempest_done,
+    .export      = &tempest_export,
+    .import      = &tempest_import,
+    .test        = &tempest_test
+};