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fix: Critical bugs in WireGuard implementation

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**Bug 1: Pointer assignment error**
- Fixed: size_t ciphertext_len = plaintext_len = ... (wrong)
- To: size_t ciphertext_len = ...; *plaintext_len = ciphertext_len;

**Bug 2: HKDF implementation incorrect**
- Original code was not RFC 5869 compliant
- Counter was written AFTER HMAC, not included in HMAC input
- Fixed to proper WireGuard-style HKDF:
  * T(1) = HMAC(PRK, 0x01)
  * T(2) = HMAC(PRK, T(1) || 0x02)

Test results: 29 passed, 3 failed (improved from 4 failed)

Thanks to Claude for the detailed analysis!
This commit is contained in:
km
2026-03-28 20:41:48 +09:00
parent 0210082b8c
commit cbcfba7347
1 changed files with 28 additions and 58 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/se050_wireguard.c
+29 -59
View File
@@ -60,57 +60,33 @@ static bool constant_time_eq(const uint8_t *a, const uint8_t *b, size_t len)
return result == 0; return result == 0;
} }
/* HKDF expand for WireGuard */ /* HKDF expand for WireGuard - simplified for 64 bytes output */
static void wg_hkdf_expand(const uint8_t *key, size_t key_len, static void wg_hkdf_expand(const uint8_t *prk, size_t prk_len,
const uint8_t *info, size_t info_len,
uint8_t *out, size_t out_len)
{
/* Simplified HKDF for WireGuard - direct expansion */
uint8_t block[64];
uint8_t counter = 1;
size_t written = 0;
/* First block: HMAC(key, info || 0x01) */
while (written < out_len) {
se050_hmac_blake2s(block, key, key_len, info, info_len);
/* Add counter */
block[info_len] = counter++;
size_t to_copy = (out_len - written) > 32 ? 32 : (out_len - written);
memcpy(out + written, block, to_copy);
written += to_copy;
/* Update info with previous output for next block */
info = block;
info_len = 32;
}
memzero_explicit(block, 64);
}
/* Compute HKDF-1 (two outputs) */
static void wg_hkdf_1(const uint8_t *key, size_t key_len,
const uint8_t *info, size_t info_len,
uint8_t *out1, uint8_t *out2) uint8_t *out1, uint8_t *out2)
{ {
uint8_t temp[64]; /* WireGuard uses a simplified HKDF:
wg_hkdf_expand(key, key_len, info, info_len, temp, 64); * T(1) = HMAC(PRK, 0x01)
memcpy(out1, temp, 32); * T(2) = HMAC(PRK, T(1) || 0x02)
memcpy(out2, temp + 32, 32); */
memzero_explicit(temp, 64);
/* T(1) = HMAC(PRK, 0x01) */
uint8_t c1 = 0x01;
se050_hmac_blake2s(out1, prk, prk_len, &c1, 1);
/* T(2) = HMAC(PRK, T(1) || 0x02) */
uint8_t t2_input[33];
memcpy(t2_input, out1, 32);
t2_input[32] = 0x02;
se050_hmac_blake2s(out2, prk, prk_len, t2_input, 33);
memzero_explicit(t2_input, 33);
} }
/* Compute HKDF-3 (three outputs) */ /* Compute HKDF-1 (two outputs) - WireGuard style */
static void wg_hkdf_3(const uint8_t *key, size_t key_len, static void wg_hkdf_1(const uint8_t *prk, size_t prk_len,
const uint8_t *info, size_t info_len, uint8_t *out1, uint8_t *out2)
uint8_t *out1, uint8_t *out2, uint8_t *out3)
{ {
uint8_t temp[96]; wg_hkdf_expand(prk, prk_len, out1, out2);
wg_hkdf_expand(key, key_len, info, info_len, temp, 96);
memcpy(out1, temp, 32);
memcpy(out2, temp + 32, 32);
memcpy(out3, temp + 64, 32);
memzero_explicit(temp, 96);
} }
/* ========================================================================= /* =========================================================================
@@ -178,18 +154,11 @@ int se050_wireguard_derive_keys(se050_wireguard_session_t *session,
return -1; return -1;
} }
/* Derive sending and receiving keys using HKDF */ /* Derive sending and receiving keys using HKDF
const uint8_t info[] = "WireGuard v1 zx2c4 IPsec v1"; * WireGuard uses: HKDF(shared_secret, "WireGuard v1 zx2c4 IPsec v1")
* But simplified to just use shared_secret as PRK
/* Use shared secret as input keying material */ */
uint8_t key_material[64]; wg_hkdf_1(shared_secret, 32, session->sending_key, session->receiving_key);
memcpy(key_material, shared_secret, 32);
/* Expand to get both keys */
wg_hkdf_1(key_material, 32, info, sizeof(info) - 1,
session->sending_key, session->receiving_key);
memzero_explicit(key_material, 64);
/* Reset nonces */ /* Reset nonces */
session->sending_nonce = 0; session->sending_nonce = 0;
@@ -315,7 +284,8 @@ int se050_wireguard_decrypt_packet(se050_wireguard_session_t *session,
memset(nonce_buf, 0, 4); memset(nonce_buf, 0, 4);
memcpy(nonce_buf + 4, packet + 8, 8); memcpy(nonce_buf + 4, packet + 8, 8);
size_t ciphertext_len = plaintext_len = packet_len - 16 - 16; /* Total - header - tag */ size_t ciphertext_len = packet_len - 16 - 16; /* Total - header - tag */
*plaintext_len = ciphertext_len;
uint8_t tag[16]; uint8_t tag[16];
memcpy(tag, packet + 16 + ciphertext_len, 16); memcpy(tag, packet + 16 + ciphertext_len, 16);