Peter Woolery
135eb3b46c
- hmac_sign now takes method+path instead of device_id; builds message as method\npath\ntimestamp\nhex(sha256(body)) per server verify_device_hmac - reporter: header renamed X-HMAC-Signature → X-Signature; passes "POST"+path - test vector regenerated against new message format; timestamp-diff test updated - .size() → .length() throughout (Arduino String has no size()) Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
74 lines
2.5 KiB
C++
74 lines
2.5 KiB
C++
// firmware/src/hmac.cpp
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#include "hmac.h"
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#include "mbedtls/md.h"
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#include <stdio.h>
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#include <string.h>
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static HString bytes_to_hex(const uint8_t* bytes, size_t len) {
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HString out;
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char buf[3];
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for (size_t i = 0; i < len; i++) {
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snprintf(buf, sizeof(buf), "%02x", bytes[i]);
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out += buf;
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}
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return out;
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}
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static void hex_to_bytes(const HString& hex, uint8_t* out, size_t out_len) {
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if (hex.length() % 2 != 0) return; // malformed — odd-length hex
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for (size_t i = 0; i < out_len && (i * 2 + 1) < hex.length(); i++) {
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char byte_str[3] = {hex[i*2], hex[i*2+1], 0};
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out[i] = (uint8_t)strtol(byte_str, nullptr, 16);
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}
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}
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static bool sha256(const uint8_t* data, size_t len, uint8_t out[32]) {
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mbedtls_md_context_t ctx;
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const mbedtls_md_info_t* info = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
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mbedtls_md_init(&ctx);
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int ret = mbedtls_md_setup(&ctx, info, 0);
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if (ret != 0) { mbedtls_md_free(&ctx); return false; }
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mbedtls_md_starts(&ctx);
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mbedtls_md_update(&ctx, data, len);
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mbedtls_md_finish(&ctx, out);
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mbedtls_md_free(&ctx);
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return true;
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}
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HString hmac_sign(const HString& secret_hex,
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const HString& method,
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const HString& path,
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uint32_t timestamp,
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const HString& body) {
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// 1. SHA256(body)
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uint8_t body_hash[32] = {};
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if (!sha256((const uint8_t*)body.c_str(), body.length(), body_hash)) {
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return HString{};
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}
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HString body_hash_hex = bytes_to_hex(body_hash, 32);
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// 2. Build message: method + "\n" + path + "\n" + timestamp + "\n" + sha256(body)
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char ts_buf[12];
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snprintf(ts_buf, sizeof(ts_buf), "%u", (unsigned)timestamp);
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HString message = method + "\n" + path + "\n" + ts_buf + "\n" + body_hash_hex;
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// 3. Decode secret from hex
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size_t secret_len = secret_hex.length() / 2;
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uint8_t secret[64] = {};
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hex_to_bytes(secret_hex, secret, secret_len);
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// 4. HMAC-SHA256(secret, message)
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uint8_t hmac_result[32];
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mbedtls_md_context_t ctx;
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const mbedtls_md_info_t* info = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
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mbedtls_md_init(&ctx);
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int ret = mbedtls_md_setup(&ctx, info, 1);
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if (ret != 0) { mbedtls_md_free(&ctx); return HString{}; }
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mbedtls_md_hmac_starts(&ctx, secret, secret_len);
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mbedtls_md_hmac_update(&ctx, (const uint8_t*)message.c_str(), message.length());
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mbedtls_md_hmac_finish(&ctx, hmac_result);
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mbedtls_md_free(&ctx);
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return bytes_to_hex(hmac_result, 32);
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}
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