First commit, Vystem v0.1

Blastproof/initfsgen/fors.c

@@ -0,0 +1,161 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "fors.h"
+#include "utils.h"
+#include "utilsx1.h"
+#include "hash.h"
+#include "thash.h"
+#include "address.h"
+
+static void fors_gen_sk(unsigned char *sk, const spx_ctx *ctx,
+                        uint32_t fors_leaf_addr[8])
+{
+    prf_addr(sk, ctx, fors_leaf_addr);
+}
+
+static void fors_sk_to_leaf(unsigned char *leaf, const unsigned char *sk,
+                            const spx_ctx *ctx,
+                            uint32_t fors_leaf_addr[8])
+{
+    thash(leaf, sk, 1, ctx, fors_leaf_addr);
+}
+
+struct fors_gen_leaf_info {
+    uint32_t leaf_addrx[8];
+};
+
+static void fors_gen_leafx1(unsigned char *leaf,
+                            const spx_ctx *ctx,
+                            uint32_t addr_idx, void *info)
+{
+    struct fors_gen_leaf_info *fors_info = info;
+    uint32_t *fors_leaf_addr = fors_info->leaf_addrx;
+
+    /* Only set the parts that the caller doesn't set */
+    set_tree_index(fors_leaf_addr, addr_idx);
+    set_type(fors_leaf_addr, SPX_ADDR_TYPE_FORSPRF);
+    fors_gen_sk(leaf, ctx, fors_leaf_addr);
+
+    set_type(fors_leaf_addr, SPX_ADDR_TYPE_FORSTREE);
+    fors_sk_to_leaf(leaf, leaf,
+                    ctx, fors_leaf_addr);
+}
+
+/**
+ * Interprets m as SPX_FORS_HEIGHT-bit unsigned integers.
+ * Assumes m contains at least SPX_FORS_HEIGHT * SPX_FORS_TREES bits.
+ * Assumes indices has space for SPX_FORS_TREES integers.
+ */
+static void message_to_indices(uint32_t *indices, const unsigned char *m)
+{
+    unsigned int i, j;
+    unsigned int offset = 0;
+
+    for (i = 0; i < SPX_FORS_TREES; i++) {
+        indices[i] = 0;
+        for (j = 0; j < SPX_FORS_HEIGHT; j++) {
+            indices[i] ^= ((m[offset >> 3] >> (offset & 0x7)) & 1u) << j;
+            offset++;
+        }
+    }
+}
+
+/**
+ * Signs a message m, deriving the secret key from sk_seed and the FTS address.
+ * Assumes m contains at least SPX_FORS_HEIGHT * SPX_FORS_TREES bits.
+ */
+void fors_sign(unsigned char *sig, unsigned char *pk,
+               const unsigned char *m,
+               const spx_ctx *ctx,
+               const uint32_t fors_addr[8])
+{
+    uint32_t indices[SPX_FORS_TREES];
+    unsigned char roots[SPX_FORS_TREES * SPX_N];
+    uint32_t fors_tree_addr[8] = {0};
+    struct fors_gen_leaf_info fors_info = {0};
+    uint32_t *fors_leaf_addr = fors_info.leaf_addrx;
+    uint32_t fors_pk_addr[8] = {0};
+    uint32_t idx_offset;
+    unsigned int i;
+
+    copy_keypair_addr(fors_tree_addr, fors_addr);
+    copy_keypair_addr(fors_leaf_addr, fors_addr);
+
+    copy_keypair_addr(fors_pk_addr, fors_addr);
+    set_type(fors_pk_addr, SPX_ADDR_TYPE_FORSPK);
+
+    message_to_indices(indices, m);
+
+    for (i = 0; i < SPX_FORS_TREES; i++) {
+        idx_offset = i * (1 << SPX_FORS_HEIGHT);
+
+        set_tree_height(fors_tree_addr, 0);
+        set_tree_index(fors_tree_addr, indices[i] + idx_offset);
+        set_type(fors_tree_addr, SPX_ADDR_TYPE_FORSPRF);
+
+        /* Include the secret key part that produces the selected leaf node. */
+        fors_gen_sk(sig, ctx, fors_tree_addr);
+        set_type(fors_tree_addr, SPX_ADDR_TYPE_FORSTREE);
+        sig += SPX_N;
+
+        /* Compute the authentication path for this leaf node. */
+        treehashx1(roots + i*SPX_N, sig, ctx,
+                 indices[i], idx_offset, SPX_FORS_HEIGHT, fors_gen_leafx1,
+                 fors_tree_addr, &fors_info);
+
+        sig += SPX_N * SPX_FORS_HEIGHT;
+    }
+
+    /* Hash horizontally across all tree roots to derive the public key. */
+    thash(pk, roots, SPX_FORS_TREES, ctx, fors_pk_addr);
+}
+
+/**
+ * Derives the FORS public key from a signature.
+ * This can be used for verification by comparing to a known public key, or to
+ * subsequently verify a signature on the derived public key. The latter is the
+ * typical use-case when used as an FTS below an OTS in a hypertree.
+ * Assumes m contains at least SPX_FORS_HEIGHT * SPX_FORS_TREES bits.
+ */
+void fors_pk_from_sig(unsigned char *pk,
+                      const unsigned char *sig, const unsigned char *m,
+                      const spx_ctx* ctx,
+                      const uint32_t fors_addr[8])
+{
+    uint32_t indices[SPX_FORS_TREES];
+    unsigned char roots[SPX_FORS_TREES * SPX_N];
+    unsigned char leaf[SPX_N];
+    uint32_t fors_tree_addr[8] = {0};
+    uint32_t fors_pk_addr[8] = {0};
+    uint32_t idx_offset;
+    unsigned int i;
+
+    copy_keypair_addr(fors_tree_addr, fors_addr);
+    copy_keypair_addr(fors_pk_addr, fors_addr);
+
+    set_type(fors_tree_addr, SPX_ADDR_TYPE_FORSTREE);
+    set_type(fors_pk_addr, SPX_ADDR_TYPE_FORSPK);
+
+    message_to_indices(indices, m);
+
+    for (i = 0; i < SPX_FORS_TREES; i++) {
+        idx_offset = i * (1 << SPX_FORS_HEIGHT);
+
+        set_tree_height(fors_tree_addr, 0);
+        set_tree_index(fors_tree_addr, indices[i] + idx_offset);
+
+        /* Derive the leaf from the included secret key part. */
+        fors_sk_to_leaf(leaf, sig, ctx, fors_tree_addr);
+        sig += SPX_N;
+
+        /* Derive the corresponding root node of this tree. */
+        compute_root(roots + i*SPX_N, leaf, indices[i], idx_offset,
+                     sig, SPX_FORS_HEIGHT, ctx, fors_tree_addr);
+        sig += SPX_N * SPX_FORS_HEIGHT;
+    }
+
+    /* Hash horizontally across all tree roots to derive the public key. */
+    thash(pk, roots, SPX_FORS_TREES, ctx, fors_pk_addr);
+}