Version v0.2.101 - Update entropy addition

nostr_chacha20.h

@@ -0,0 +1,115 @@
+/*
+ * nostr_chacha20.h - ChaCha20 stream cipher implementation
+ * 
+ * Implementation based on RFC 8439 "ChaCha20 and Poly1305 for IETF Protocols"
+ * 
+ * This is a small, portable implementation for NIP-44 support in the NOSTR library.
+ * The implementation prioritizes correctness and simplicity over performance.
+ */
+
+#ifndef NOSTR_CHACHA20_H
+#define NOSTR_CHACHA20_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * ============================================================================
+ * CONSTANTS AND DEFINITIONS
+ * ============================================================================
+ */
+
+#define CHACHA20_KEY_SIZE    32  /* 256 bits */
+#define CHACHA20_NONCE_SIZE  12  /* 96 bits */
+#define CHACHA20_BLOCK_SIZE  64  /* 512 bits */
+
+/*
+ * ============================================================================
+ * CORE CHACHA20 FUNCTIONS
+ * ============================================================================
+ */
+
+/**
+ * ChaCha20 quarter round operation
+ * 
+ * Operates on four 32-bit words performing the core ChaCha20 quarter round:
+ * a += b; d ^= a; d <<<= 16;
+ * c += d; b ^= c; b <<<= 12;
+ * a += b; d ^= a; d <<<= 8;
+ * c += d; b ^= c; b <<<= 7;
+ * 
+ * @param state[in,out] ChaCha state as 16 32-bit words
+ * @param a, b, c, d    Indices into state array for quarter round
+ */
+void chacha20_quarter_round(uint32_t state[16], int a, int b, int c, int d);
+
+/**
+ * ChaCha20 block function
+ * 
+ * Transforms a 64-byte input block using ChaCha20 algorithm with 20 rounds.
+ * 
+ * @param key[in]       32-byte key
+ * @param counter[in]   32-bit block counter
+ * @param nonce[in]     12-byte nonce
+ * @param output[out]   64-byte output buffer
+ * @return              0 on success, negative on error
+ */
+int chacha20_block(const uint8_t key[32], uint32_t counter, 
+                   const uint8_t nonce[12], uint8_t output[64]);
+
+/**
+ * ChaCha20 encryption/decryption
+ * 
+ * Encrypts or decrypts data using ChaCha20 stream cipher.
+ * Since ChaCha20 is a stream cipher, encryption and decryption are the same operation.
+ * 
+ * @param key[in]           32-byte key
+ * @param counter[in]       Initial 32-bit counter value
+ * @param nonce[in]         12-byte nonce
+ * @param input[in]         Input data to encrypt/decrypt
+ * @param output[out]       Output buffer (can be same as input)
+ * @param length[in]        Length of input data in bytes
+ * @return                  0 on success, negative on error
+ */
+int chacha20_encrypt(const uint8_t key[32], uint32_t counter, 
+                     const uint8_t nonce[12], const uint8_t* input, 
+                     uint8_t* output, size_t length);
+
+/*
+ * ============================================================================
+ * UTILITY FUNCTIONS
+ * ============================================================================
+ */
+
+/**
+ * Initialize ChaCha20 state matrix
+ * 
+ * Sets up the initial 16-word state matrix with constants, key, counter, and nonce.
+ * 
+ * @param state[out]    16-word state array to initialize
+ * @param key[in]       32-byte key
+ * @param counter[in]   32-bit block counter
+ * @param nonce[in]     12-byte nonce
+ */
+void chacha20_init_state(uint32_t state[16], const uint8_t key[32], 
+                         uint32_t counter, const uint8_t nonce[12]);
+
+/**
+ * Serialize ChaCha20 state to bytes
+ * 
+ * Converts 16 32-bit words to 64 bytes in little-endian format.
+ * 
+ * @param state[in]     16-word state array
+ * @param output[out]   64-byte output buffer
+ */
+void chacha20_serialize_state(const uint32_t state[16], uint8_t output[64]);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* NOSTR_CHACHA20_H */