mirror of
https://github.com/AGWA/git-crypt.git
synced 2025-12-05 20:40:05 -08:00
86 lines
2.5 KiB
C++
86 lines
2.5 KiB
C++
#define _BSD_SOURCE
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#include "crypto.hpp"
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#include <openssl/aes.h>
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#include <openssl/sha.h>
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#include <openssl/hmac.h>
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#include <openssl/evp.h>
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#include <fstream>
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#include <iostream>
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#include <cstring>
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#include <cstdlib>
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#include <endian.h>
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void load_keys (const char* filepath, keys_t* keys)
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{
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std::ifstream file(filepath);
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if (!file) {
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perror(filepath);
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std::exit(1);
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}
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char buffer[AES_KEY_BITS/8 + HMAC_KEY_LEN];
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file.read(buffer, sizeof(buffer));
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if (file.gcount() != sizeof(buffer)) {
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std::clog << filepath << ": Premature end of key file\n";
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std::exit(1);
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}
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// First comes the AES encryption key
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if (AES_set_encrypt_key(reinterpret_cast<uint8_t*>(buffer), AES_KEY_BITS, &keys->enc) != 0) {
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std::clog << filepath << ": Failed to initialize AES encryption key\n";
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std::exit(1);
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}
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// Then it's the HMAC key
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memcpy(keys->hmac, buffer + AES_KEY_BITS/8, HMAC_KEY_LEN);
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}
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aes_ctr_state::aes_ctr_state (const uint8_t* arg_nonce, size_t arg_nonce_len)
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{
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memset(nonce, '\0', sizeof(nonce));
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memcpy(nonce, arg_nonce, std::min(arg_nonce_len, sizeof(nonce)));
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byte_counter = 0;
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memset(otp, '\0', sizeof(otp));
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}
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void aes_ctr_state::process_block (const AES_KEY* key, const uint8_t* in, uint8_t* out, size_t len)
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{
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for (size_t i = 0; i < len; ++i) {
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if (byte_counter % 16 == 0) {
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// Generate a new OTP
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// CTR value:
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// first 12 bytes - nonce
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// last 4 bytes - block number (sequentially increasing with each block)
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uint8_t ctr[16];
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uint32_t blockno = htole32(byte_counter / 16);
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memcpy(ctr, nonce, 12);
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memcpy(ctr + 12, &blockno, 4);
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AES_encrypt(ctr, otp, key);
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}
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// encrypt one byte
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out[i] = in[i] ^ otp[byte_counter++ % 16];
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}
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}
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// Compute HMAC-SHA1-96 (i.e. first 96 bits of HMAC-SHA1) for the given buffer with the given key
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void hmac_sha1_96 (uint8_t* out, const uint8_t* buffer, size_t buffer_len, const uint8_t* key, size_t key_len)
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{
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uint8_t full_digest[20];
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HMAC(EVP_sha1(), key, key_len, buffer, buffer_len, full_digest, NULL);
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memcpy(out, full_digest, 12); // Truncate to first 96 bits
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}
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// Encrypt/decrypt an entire input stream, writing to the given output stream
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void process_stream (std::istream& in, std::ostream& out, const AES_KEY* enc_key, const uint8_t* nonce)
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{
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aes_ctr_state state(nonce, 12);
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uint8_t buffer[1024];
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while (in) {
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in.read(reinterpret_cast<char*>(buffer), sizeof(buffer));
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state.process_block(enc_key, buffer, buffer, in.gcount());
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out.write(reinterpret_cast<char*>(buffer), in.gcount());
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}
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}
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