The WvdS Crypto Service implements several protection mechanisms that are automatically active. You don't need to configure anything.

Protects against Denial-of-Service (DoS) attacks through overload.

Behavior when exceeded:

Request --> [Rate Limiter] --> Status: 0x07 (RATE_LIMITED)
                           --> No crypto operation performed

Client Recommendation:

• On Status 0x07: Wait and retry with backoff
• Exponential wait time: 100ms, 200ms, 400ms, …

int send_with_retry(const uint8_t* request, size_t len) {
    int retry = 0;
    int delay_ms = 100;
 
    while (retry < 5) {
        send_request(request, len);
        int status = get_response_status();
 
        if (status != 0x07) return status;  // Not rate-limited
 
        usleep(delay_ms * 1000);
        delay_ms *= 2;  // Exponential backoff
        retry++;
    }
    return -1;  // Timeout
}

The Crypto Service actively protects against nonce reuse:

• Nonce is generated by the service (CSPRNG)
• Client cannot provide their own nonce
• Each nonce is used only once

• Service stores used nonces (Bloom Filter)
• On repeated nonce: Status 0x08 (NONCE_REUSE)
• Window size: 1 million nonces

Note: Nonce tracking is per Key-ID. The tracker is reset on key rotation.

All inputs are validated before processing:

No Exceptions:

The service doesn't throw exceptions. All errors are returned via status codes.

Reasons:

• Shared memory size limited
• DoS protection (memory exhaustion)
• Predictable runtime

Encrypting large data:

// Chunked Encryption for large files
#define CHUNK_SIZE (60 * 1024)  // 60 KB per chunk
 
int encrypt_large_file(FILE* in, FILE* out) {
    uint8_t buffer[CHUNK_SIZE];
    size_t bytes_read;
    uint32_t chunk_id = 0;
 
    while ((bytes_read = fread(buffer, 1, CHUNK_SIZE, in)) > 0) {
        // AAD contains Chunk-ID for ordering protection
        char aad[32];
        snprintf(aad, sizeof(aad), "chunk:%u", chunk_id++);
 
        uint8_t ct[CHUNK_SIZE + 28];
        size_t ct_len;
        uint8_t nonce[12], tag[16];
 
        encrypt_message(buffer, bytes_read, aad, strlen(aad),
                       ct, &ct_len, nonce, tag);
 
        fwrite(nonce, 1, 12, out);
        fwrite(tag, 1, 16, out);
        fwrite(ct, 1, ct_len, out);
    }
    return 0;
}

All security-critical data is overwritten after use:

• Keys (after crypto operation)
• Plaintexts (after encryption)
• Shared Secrets (after key exchange)

Implementation:

// Prevent compiler optimization
static void secure_zero(void* ptr, size_t len) {
    volatile uint8_t* p = (volatile uint8_t*)ptr;
    while (len--) *p++ = 0;
}

The Crypto Service runs as an isolated L4Re task:

+---------------------------------------------------------------+
|                    L4Re Microkernel                           |
+---------------------------------------------------------------+
|     |              |              |              |            |
|  +--+--+       +---+---+      +---+---+      +---+---+        |
|  | Sigma0 |    | Moe   |      | Crypto |     | OEM   |        |
|  | (Root) |    | (Mem) |      | Service|     | Gateway|       |
|  +--------+    +-------+      +--------+     +--------+        |
|                                   |              |             |
|                                   +--------------+             |
|                                   ONLY this IPC                |
+---------------------------------------------------------------+

Security Guarantees:

• Own address space (no direct memory access)
• Only explicit IPC allowed (capability-based)
• No network access (air-gapped)

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