initial commit

2026-08-27 11:03:10 -06:00
commit d164820ea9
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+#ifndef ZERIN_CRYPTO_H
+#define ZERIN_CRYPTO_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+#define CRYPTO_KEY_SIZE     32
+#define CRYPTO_NONCE_SIZE   12
+#define CRYPTO_TAG_SIZE     16
+#define CRYPTO_SHA256_SIZE  32
+#define CRYPTO_X25519_KEY   32
+
+// ============================================================================
+// Random
+// ============================================================================
+int crypto_random_bytes(uint8_t *buf, size_t len);
+double crypto_random_float(void);  // [0.0, 1.0)
+
+// ============================================================================
+// SHA-256
+// ============================================================================
+typedef struct {
+    uint32_t state[8];
+    uint64_t bitcount;
+    uint8_t  buffer[64];
+    uint32_t buflen;
+} sha256_ctx_t;
+
+void sha256_init(sha256_ctx_t *ctx);
+void sha256_update(sha256_ctx_t *ctx, const uint8_t *data, size_t len);
+void sha256_final(sha256_ctx_t *ctx, uint8_t out[32]);
+void sha256(const uint8_t *data, size_t len, uint8_t out[32]);
+
+// HMAC-SHA256
+void hmac_sha256(const uint8_t *key, size_t key_len,
+                 const uint8_t *data, size_t data_len,
+                 uint8_t out[32]);
+
+// ============================================================================
+// HKDF (RFC 5869)
+// ============================================================================
+int hkdf_extract(const uint8_t *salt, size_t salt_len,
+                 const uint8_t *ikm, size_t ikm_len,
+                 uint8_t prk[32]);
+
+int hkdf_expand(const uint8_t prk[32],
+                const uint8_t *info, size_t info_len,
+                uint8_t *okm, size_t okm_len);
+
+int hkdf_derive(const uint8_t *salt, size_t salt_len,
+                const uint8_t *ikm, size_t ikm_len,
+                const uint8_t *info, size_t info_len,
+                uint8_t *okm, size_t okm_len);
+
+// ============================================================================
+// X25519 (RFC 7748)
+// ============================================================================
+void x25519_clamp(uint8_t key[32]);
+int  x25519_keygen(uint8_t privkey[32], uint8_t pubkey[32]);
+int  x25519_shared_secret(const uint8_t privkey[32],
+                          const uint8_t peer_pubkey[32],
+                          uint8_t shared[32]);
+
+// ============================================================================
+// ChaCha20 (RFC 8439)
+// ============================================================================
+typedef struct {
+    uint32_t state[16];
+} chacha20_ctx_t;
+
+void chacha20_init(chacha20_ctx_t *ctx, const uint8_t key[32],
+                   const uint8_t nonce[12], uint32_t counter);
+void chacha20_encrypt(chacha20_ctx_t *ctx, const uint8_t *in,
+                      uint8_t *out, size_t len);
+
+// ============================================================================
+// Poly1305 (RFC 8439)
+// ============================================================================
+typedef struct {
+    uint32_t r[5];
+    uint32_t h[5];
+    uint32_t pad[4];
+    uint8_t  buffer[16];
+    size_t   buflen;
+    size_t   total;
+} poly1305_ctx_t;
+
+void poly1305_init(poly1305_ctx_t *ctx, const uint8_t key[32]);
+void poly1305_update(poly1305_ctx_t *ctx, const uint8_t *data, size_t len);
+void poly1305_final(poly1305_ctx_t *ctx, uint8_t tag[16]);
+
+// ============================================================================
+// ChaCha20-Poly1305 AEAD (RFC 8439)
+// ============================================================================
+
+// Encrypt: returns ciphertext_len (plaintext_len + 16 for tag)
+// out must have room for plaintext_len + CRYPTO_TAG_SIZE
+int aead_encrypt(const uint8_t key[32], const uint8_t nonce[12],
+                 const uint8_t *aad, size_t aad_len,
+                 const uint8_t *plaintext, size_t plaintext_len,
+                 uint8_t *out);
+
+// Decrypt: returns 0 on success, -1 on auth failure
+// out must have room for ciphertext_len - CRYPTO_TAG_SIZE
+int aead_decrypt(const uint8_t key[32], const uint8_t nonce[12],
+                 const uint8_t *aad, size_t aad_len,
+                 const uint8_t *ciphertext, size_t ciphertext_len,
+                 uint8_t *out);
+
+// ============================================================================
+// Key Exchange
+// ============================================================================
+typedef struct {
+    uint8_t agent_pubkey_hash[32];  // SHA256(agent_pubkey)
+    uint8_t ephemeral_pubkey[32];
+    uint8_t ephemeral_privkey[32];  // NOT sent
+    uint8_t session_key[32];
+} key_exchange_t;
+
+int key_exchange_init(key_exchange_t *kx, const uint8_t agent_pubkey[32]);
+int key_exchange_derive(key_exchange_t *kx, const uint8_t server_pubkey[32]);
+
+// ============================================================================
+// Utility
+// ============================================================================
+void secure_zero(void *ptr, size_t len);
+int  constant_time_compare(const uint8_t *a, const uint8_t *b, size_t len);
+
+#endif // ZERIN_CRYPTO_H