debug: Add debug output for ChaCha20-Poly1305

Found: TAG mismatch between encrypt and decrypt
- Encrypt produces: b3a7f2c8...
- Decrypt expects: f6e6610c...

Root cause: Likely AAD processing difference
Need to compare encrypt/decrypt paths in detail.

WireGuard tests: 28 passed, 4 failed

src/se050_chacha20_poly1305.c

@@ -8,6 +8,7 @@
 #include "se050_chacha20_poly1305.h"
 #include "se050_crypto_utils.h"
 #include <string.h>
+#include <stdio.h>
 
 /* ESP32 detection */
 #if defined(ESP_PLATFORM) || defined(__XTENSA__) || defined(__riscv)
@@ -694,6 +695,12 @@ int se050_chacha20_poly1305_decrypt(se050_chacha20_poly1305_ctx_t *ctx,
     /* Constant-time comparison */
     int ret = 0;
     if (crypto_memneq(expected_tag, tag, 16) != 0) {
+        fprintf(stderr, "DEBUG: tag mismatch\n");
+        fprintf(stderr, "Expected: ");
+        for(int i=0; i<16; i++) fprintf(stderr, "%02x", expected_tag[i]);
+        fprintf(stderr, "\nGot:      ");
+        for(int i=0; i<16; i++) fprintf(stderr, "%02x", tag[i]);
+        fprintf(stderr, "\n");
         ret = -1;
     }
     

src/se050_wireguard.c

@@ -23,6 +23,7 @@
 #include <string.h>
 #include <stdint.h>
 #include <stdlib.h>
+#include <stdio.h>
 
 /* =========================================================================
  * WireGuard Protocol Constants
@@ -322,6 +323,8 @@ int se050_wireguard_decrypt_packet(se050_wireguard_session_t *session,
     memzero_explicit(tag, 16);
     
     if (ret < 0) {
+        fprintf(stderr, "DEBUG: decrypt failed, ciphertext_len=%zu, packet_len=%zu, aad_len=16\n", 
+                ciphertext_len, packet_len);
         return -1;
     }
     

tests/test_debug_wg.c

@@ -0,0 +1,54 @@
+#define X25519_SW_TEST 1
+#include "se050_wireguard.h"
+#include "se050_x25519_sw.h"
+#include "se050_chacha20_poly1305.h"
+#include <stdio.h>
+#include <string.h>
+
+int main() {
+    printf("=== Debug WireGuard Encrypt/Decrypt ===\n\n");
+    
+    uint8_t priv[32], peer_pub[32];
+    for(int i=0; i<32; i++) { priv[i] = i+1; peer_pub[i] = i+2; }
+    
+    se050_wireguard_session_t session;
+    se050_wireguard_session_init(&session, priv, peer_pub);
+    
+    uint8_t ss[32] = {0};
+    for(int i=0; i<32; i++) ss[i] = i;
+    se050_wireguard_derive_keys(&session, ss);
+    
+    printf("Sending key (first 8): ");
+    for(int i=0; i<8; i++) printf("%02x", session.sending_key[i]);
+    printf("\n");
+    
+    printf("Receiving key (first 8): ");
+    for(int i=0; i<8; i++) printf("%02x", session.receiving_key[i]);
+    printf("\n\n");
+    
+    const char *plaintext = "test";
+    uint8_t encrypted[100];
+    size_t enc_len;
+    
+    printf("=== Encrypt ===\n");
+    int ret = se050_wireguard_encrypt_packet(&session, encrypted, &enc_len, (uint8_t*)plaintext, 4);
+    printf("Encrypt result: %d\n", ret);
+    printf("Encrypted length: %zu\n", enc_len);
+    printf("Encrypted (hex): ");
+    for(size_t i=0; i<enc_len; i++) printf("%02x", encrypted[i]);
+    printf("\n\n");
+    
+    printf("=== Decrypt ===\n");
+    uint8_t decrypted[100];
+    size_t dec_len;
+    ret = se050_wireguard_decrypt_packet(&session, decrypted, &dec_len, encrypted, enc_len);
+    printf("Decrypt result: %d\n", ret);
+    printf("Decrypted length: %zu\n", dec_len);
+    if (ret == 0) {
+        printf("Decrypted content: %.*s\n", (int)dec_len, decrypted);
+    } else {
+        printf("Decrypt FAILED!\n");
+    }
+    
+    return 0;
+}