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protocol: Make T_DATUM_PROTOCOL_HEADER serialisation explicit #185

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protocol: Make T_DATUM_PROTOCOL_HEADER serialisation explicit #185

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64 changes: 41 additions & 23 deletions src/datum_protocol.c
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Original file line number Diff line number Diff line change
Expand Up @@ -149,10 +149,6 @@ unsigned char datum_protocol_setup_new_job_idx(void *sx) {
return a;
}

static inline void datum_xor_header_key(void *h, uint32_t key) {
*((uint32_t *)h) ^= key;
}

uint32_t datum_header_xor_feedback(const uint32_t i) {
uint32_t s = 0xb10cfeed;
uint32_t h = s;
Expand All @@ -172,6 +168,32 @@ uint32_t datum_header_xor_feedback(const uint32_t i) {
return h;
}

static
void datum_header_pk(uint8_t * const dst, const size_t offset, const T_DATUM_PROTOCOL_HEADER * const h, uint32_t * const xor_key) {
uint32_t raw = (h->cmd_len & 0x3fffffUL) |
((uint32_t)h->is_signed << 24) |
((uint32_t)h->is_encrypted_pubkey << 25) |
((uint32_t)h->is_encrypted_channel << 26) |
((uint32_t)(h->proto_cmd & 0x1f) << 27);
raw ^= *xor_key;
*xor_key = datum_header_xor_feedback(*xor_key);

pk_u32le(dst, offset, raw);
}

static
void datum_header_upk(T_DATUM_PROTOCOL_HEADER * const h, const uint8_t * const src, const size_t offset, uint32_t * const xor_key) {
uint32_t raw = upk_u32le(src, offset);
raw ^= *xor_key;
*xor_key = datum_header_xor_feedback(*xor_key);

h->cmd_len = raw & 0x003fffffUL;
h->is_signed = raw & 0x01000000UL;
h->is_encrypted_pubkey = raw & 0x02000000UL;
h->is_encrypted_channel = raw & 0x04000000UL;
h->proto_cmd = (raw >> 27) & 0x1f;
}

// Take the hexidecimal public key string and store it in a DATUM_ENC_KEYS
int datum_pubkey_to_struct(const char *input, DATUM_ENC_KEYS *key) {
int i;
Expand Down Expand Up @@ -229,6 +251,7 @@ int datum_protocol_mining_cmd(void *data, int len) {
// encypt and send a standard mining sub-command
// this can be called from other threads so must be thread safe!
T_DATUM_PROTOCOL_HEADER h;
unsigned char wire_h[T_DATUM_PROTOCOL_HEADER_WIRE_BYTES];
int i;

memset(&h, 0, sizeof(T_DATUM_PROTOCOL_HEADER));
Expand All @@ -244,11 +267,10 @@ int datum_protocol_mining_cmd(void *data, int len) {

crypto_box_easy_afternm(data, data, len, session_nonce_sender, session_precomp.precomp_remote);
//DLOG_DEBUG("mining cmd 5--- len %d, send header key %8.8x, raw %8.8lx", h.cmd_len, sending_header_key, (unsigned long)upk_u32le(h, 0));
datum_xor_header_key(&h, sending_header_key);
sending_header_key = datum_header_xor_feedback(sending_header_key);
datum_header_pk(wire_h, 0, &h, &sending_header_key);
datum_increment_session_nonce(session_nonce_sender);

i = datum_protocol_chars_to_server((unsigned char *)&h, sizeof(T_DATUM_PROTOCOL_HEADER));
i = datum_protocol_chars_to_server(wire_h, sizeof(wire_h));
if (i < 1) {
pthread_mutex_unlock(&datum_protocol_sender_stage1_lock);
return -1;
Expand Down Expand Up @@ -1038,16 +1060,12 @@ int datum_protocol_send_hello(int sockfd) {
i+=crypto_sign_BYTES;

// seal it up
crypto_box_seal(&enc_hello_msg[sizeof(T_DATUM_PROTOCOL_HEADER)], hello_msg, i, pool_keys.pk_x25519);
crypto_box_seal(&enc_hello_msg[T_DATUM_PROTOCOL_HEADER_WIRE_BYTES], hello_msg, i, pool_keys.pk_x25519);
i+=crypto_box_SEALBYTES;

h.cmd_len = i;

memcpy(enc_hello_msg, &h, sizeof(T_DATUM_PROTOCOL_HEADER));

// apply our initial xor key to the header, just to obfuscate it a tiny bit
// kinda pointless, but ok
datum_xor_header_key(&enc_hello_msg[0], sending_header_key);
datum_header_pk(enc_hello_msg, 0, &h, &sending_header_key);

DLOG_DEBUG("Sending handshake init (%d bytes)", h.cmd_len);

Expand All @@ -1070,7 +1088,7 @@ int datum_protocol_send_hello(int sockfd) {
// FIXME: why is this mixed-endian?
//DLOG_DEBUG("Session Nonce: %8.8X%8.8X%8.8X%8.8X%8.8X%8.8X", upk_u32le(session_nonce_receiver, 0), upk_u32le(session_nonce_receiver, 4), upk_u32le(session_nonce_receiver, 8), upk_u32le(session_nonce_receiver, 12), upk_u32le(session_nonce_receiver, 16), upk_u32le(session_nonce_receiver, 20));

return datum_protocol_chars_to_server(enc_hello_msg, i+sizeof(T_DATUM_PROTOCOL_HEADER));
return datum_protocol_chars_to_server(enc_hello_msg, T_DATUM_PROTOCOL_HEADER_WIRE_BYTES + i);
}

int datum_protocol_decrypt_sealed(T_DATUM_PROTOCOL_HEADER *h, unsigned char *data) {
Expand Down Expand Up @@ -1464,6 +1482,7 @@ void *datum_protocol_client(void *args) {
bool break_again = false;
int sent = 0;
T_DATUM_PROTOCOL_HEADER s_header;
unsigned char wire_h[T_DATUM_PROTOCOL_HEADER_WIRE_BYTES];

pthread_rwlock_wrlock(&datum_jobs_rwlock);
for(i=0;i<MAX_DATUM_PROTOCOL_JOBS;i++) {
Expand Down Expand Up @@ -1709,7 +1728,7 @@ void *datum_protocol_client(void *args) {
case 1:
case 2:
case 3: {
n = recv(sockfd, ((unsigned char *)&s_header) + (sizeof(T_DATUM_PROTOCOL_HEADER) - protocol_state), protocol_state, MSG_DONTWAIT);
n = recv(sockfd, &wire_h[sizeof(wire_h) - protocol_state], protocol_state, MSG_DONTWAIT);
if (n <= 0) {
if ((n < 0) && ((errno == EAGAIN || errno == EWOULDBLOCK))) {
continue;
Expand All @@ -1718,34 +1737,34 @@ void *datum_protocol_client(void *args) {
break_again = true; break;
}

if ((n+(sizeof(T_DATUM_PROTOCOL_HEADER) - protocol_state)) != sizeof(T_DATUM_PROTOCOL_HEADER)) {
if ((n + (sizeof(wire_h) - protocol_state)) != sizeof(wire_h)) {
if ((n+protocol_state) > 4) {
DLOG_DEBUG("recv() issue. too many header bytes. protocol_state=%d, n=%d, errno=%d (%s)", protocol_state, n, errno, strerror(errno));
break_again = true; break;
Comment on lines +1740 to 1743
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Copilot AI Apr 6, 2026

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This check uses a hard-coded header size (4). Since the header size is now abstracted via wire_h/T_DATUM_PROTOCOL_HEADER_WIRE_BYTES, use sizeof(wire_h) (or the macro) here too to avoid future inconsistencies if the wire header size changes.

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}

protocol_state = sizeof(T_DATUM_PROTOCOL_HEADER) - n - (sizeof(T_DATUM_PROTOCOL_HEADER) - protocol_state); // should give us a state equal to the number of. consoluted to show the process. (compiler optimizes)
protocol_state = sizeof(wire_h) - n - (sizeof(wire_h) - protocol_state); // should give us a state equal to the number of. consoluted to show the process. (compiler optimizes)
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Typo in comment: “consoluted” should be “convoluted”.

Suggested change
protocol_state = sizeof(wire_h) - n - (sizeof(wire_h) - protocol_state); // should give us a state equal to the number of. consoluted to show the process. (compiler optimizes)
protocol_state = sizeof(wire_h) - n - (sizeof(wire_h) - protocol_state); // should give us a state equal to the number of. convoluted to show the process. (compiler optimizes)

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continue;
}

protocol_state = 4;
continue; // cant fall through to 0, so loop around back to this to jump to 4
}
case 0: {
n = recv(sockfd, &s_header, sizeof(T_DATUM_PROTOCOL_HEADER), MSG_DONTWAIT);
n = recv(sockfd, &wire_h[0], sizeof(wire_h), MSG_DONTWAIT);
if (n <= 0) {
if ((n < 0) && ((errno == EAGAIN || errno == EWOULDBLOCK))) {
continue;
}
DLOG_DEBUG("recv() issue. protocol_state=%d, n=%d, errno=%d (%s)", protocol_state, n, errno, strerror(errno));
break_again = true; break;
}
if (n != sizeof(T_DATUM_PROTOCOL_HEADER)) {
if (n != sizeof(wire_h)) {
if (n > 4) {
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Copilot AI Apr 6, 2026

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This branch still hard-codes 4 as the maximum header byte count. For consistency with the rest of this state machine, replace it with sizeof(wire_h) (or T_DATUM_PROTOCOL_HEADER_WIRE_BYTES).

Suggested change
if (n > 4) {
if (n > sizeof(wire_h)) {

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DLOG_DEBUG("recv() issue. too many header bytes (B). protocol_state=%d, n=%d, errno=%d (%s)", protocol_state, n, errno, strerror(errno));
break_again = true; break;
}
protocol_state = sizeof(T_DATUM_PROTOCOL_HEADER)-n;
protocol_state = sizeof(wire_h) - n;
continue;
}

Expand All @@ -1755,9 +1774,8 @@ void *datum_protocol_client(void *args) {
}

case 4: {
datum_xor_header_key(&s_header, receiving_header_key);
//DLOG_DEBUG("Server CMD: cmd=%u, len=%u, raw = %8.8x ... rkey = %8.8x", s_header.proto_cmd, s_header.cmd_len, upk_u32le(s_header, 0), receiving_header_key);
receiving_header_key = datum_header_xor_feedback(receiving_header_key);
datum_header_upk(&s_header, wire_h, 0, &receiving_header_key);
//DLOG_DEBUG("Server CMD: cmd=%u, len=%u, raw = %8.8x ... rkey(after) = %8.8x", s_header.proto_cmd, s_header.cmd_len, upk_u32le(s_header, 0), receiving_header_key);
protocol_state = 5;
server_in_buf = 0;
if (!s_header.cmd_len) {
Expand Down
10 changes: 5 additions & 5 deletions src/datum_protocol.h
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Original file line number Diff line number Diff line change
Expand Up @@ -58,14 +58,14 @@
// It's likely possible to brute force the XOR key to break packets down into individual commands, but the contents and nature of the
// cmd is still obfuscated and unrecoverable without the session keys.

typedef struct __attribute__((packed)) T_DATUM_PROTOCOL_HEADER {
typedef struct T_DATUM_PROTOCOL_HEADER {
uint32_t cmd_len:22; // max cmd size is 2^22 (~4MB), which is roughly the max block size for a raw submission or a raw template validation
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uint8_t reserved:2; // save for later use
bool is_signed:1;
bool is_encrypted_pubkey:1;
bool is_encrypted_channel:1;
bool is_signed;
bool is_encrypted_pubkey;
bool is_encrypted_channel;
uint8_t proto_cmd:5; // 32 protocol level commands
} T_DATUM_PROTOCOL_HEADER;
#define T_DATUM_PROTOCOL_HEADER_WIRE_BYTES 4

typedef struct {
bool is_remote;
Expand Down
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