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Added SHA command to ATSHA204 backend driver

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The SHA command is available in ATSHA204A variants of the chip
and can be used to calculate SHA256 digests of arbitrary data.

This enables us to strengthen the quality of the signatures by
salting signatures with node-specific data and improving the
quality of random data.
This commit is contained in:
Patrick Fallberg
2015-03-16 20:14:22 +01:00
parent cb5e3172bd
commit 4c4c9a8b39
4 changed files with 54 additions and 6 deletions
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libraries/MySensors/MySigningAtsha204.cpp
+26
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@@ -215,3 +215,29 @@ bool MySigningAtsha204::calculateSignature(MyMessage &msg) {
DEBUG_ATSHA_PRINTBUF("HMAC:", &rx_buffer[SHA204_BUFFER_POS_DATA], 32);
return true; // We return with the signature in rx_buffer[SHA204_BUFFER_POS_DATA]
}
// Helper to calculate a generic SHA256 digest of provided buffer (returned in rx_buffer[SHA204_BUFFER_POS_DATA]) (only supports one block)
uint8_t* MySigningAtsha204::sha256(const uint8_t* data, size_t sz) {
// Initiate SHA256 calculator
if (atsha204.sha204m_execute(SHA204_SHA, SHA_INIT, 0, 0, NULL,
SHA_COUNT_SHORT, tx_buffer, SHA_RSP_SIZE_SHORT, rx_buffer) != SHA204_SUCCESS) {
DEBUG_ATSHA_PRINTLN("Failed to initiate sha256");
return NULL;
}
// Calculate a hash
memset(temp_message, 0x00, SHA_MSG_SIZE);
memcpy(temp_message, data, sz);
temp_message[sz] = 0x80;
// Write length data to the last bytes
temp_message[SHA_MSG_SIZE-2] = (sz >> 5);
temp_message[SHA_MSG_SIZE-1] = (sz << 3);
DEBUG_ATSHA_PRINTBUF("Data to hash (padded):", temp_message, SHA_MSG_SIZE);
if (atsha204.sha204m_execute(SHA204_SHA, SHA_CALC, 0, SHA_MSG_SIZE, temp_message,
SHA_COUNT_LONG, tx_buffer, SHA_RSP_SIZE_LONG, rx_buffer) != SHA204_SUCCESS) {
DEBUG_ATSHA_PRINTLN("Failed to calculate sha256");
return NULL;
}
DEBUG_ATSHA_PRINTBUF("SHA:", &rx_buffer[SHA204_BUFFER_POS_DATA], 32);
return &rx_buffer[SHA204_BUFFER_POS_DATA];
}