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Initial commit: wowee native WoW 3.3.5a client
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docs/srp-implementation.md
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docs/srp-implementation.md
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# SRP Authentication Implementation
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## Overview
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The SRP (Secure Remote Password) authentication system has been fully implemented for World of Warcraft 3.3.5a compatibility. This implementation follows the SRP6a protocol as used by the original wowee client.
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## Components
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### 1. BigNum (`include/auth/big_num.hpp`)
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Wrapper around OpenSSL's BIGNUM for arbitrary-precision integer arithmetic.
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**Key Features:**
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- Little-endian byte array conversion (WoW protocol requirement)
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- Modular exponentiation (critical for SRP)
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- All standard arithmetic operations
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- Random number generation
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**Usage Example:**
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```cpp
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// Create from bytes (little-endian)
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std::vector<uint8_t> bytes = {0x01, 0x02, 0x03};
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BigNum num(bytes, true);
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// Modular exponentiation: result = base^exp mod N
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BigNum result = base.modPow(exponent, modulus);
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// Convert back to bytes
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std::vector<uint8_t> output = num.toArray(true, 32); // 32 bytes, little-endian
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```
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### 2. SRP (`include/auth/srp.hpp`)
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Complete SRP6a authentication implementation.
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## Authentication Flow
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### Phase 1: Initialization
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```cpp
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#include "auth/srp.hpp"
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SRP srp;
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srp.initialize("username", "password");
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```
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**What happens:**
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- Stores credentials for later use
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- Marks SRP as initialized
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### Phase 2: Server Challenge Processing
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When you receive the `LOGON_CHALLENGE` response from the auth server:
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```cpp
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// Extract from server packet:
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std::vector<uint8_t> B; // 32 bytes - server public ephemeral
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std::vector<uint8_t> g; // Usually 1 byte (0x02)
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std::vector<uint8_t> N; // 256 bytes - prime modulus
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std::vector<uint8_t> salt; // 32 bytes - salt
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// Feed to SRP
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srp.feed(B, g, N, salt);
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```
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**What happens internally:**
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1. Stores server values (B, g, N, salt)
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2. Computes `x = H(salt | H(username:password))`
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3. Generates random client ephemeral `a` (19 bytes)
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4. Computes `A = g^a mod N`
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5. Computes scrambler `u = H(A | B)`
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6. Computes session key `S = (B - 3*g^x)^(a + u*x) mod N`
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7. Splits S, hashes halves, interleaves to create `K` (40 bytes)
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8. Computes client proof `M1 = H(H(N)^H(g) | H(username) | salt | A | B | K)`
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9. Pre-computes server proof `M2 = H(A | M1 | K)`
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### Phase 3: Sending Client Proof
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Send `LOGON_PROOF` packet to server:
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```cpp
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// Get values to send in packet
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std::vector<uint8_t> A = srp.getA(); // 32 bytes
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std::vector<uint8_t> M1 = srp.getM1(); // 20 bytes
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// Build LOGON_PROOF packet:
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// - A (32 bytes)
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// - M1 (20 bytes)
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// - CRC (20 bytes of zeros)
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// - Number of keys (1 byte: 0)
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// - Security flags (1 byte: 0)
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```
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### Phase 4: Server Proof Verification
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When you receive `LOGON_PROOF` response:
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```cpp
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// Extract M2 from server response (20 bytes)
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std::vector<uint8_t> serverM2; // From packet
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// Verify
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if (srp.verifyServerProof(serverM2)) {
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LOG_INFO("Authentication successful!");
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// Get session key for encryption
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std::vector<uint8_t> K = srp.getSessionKey(); // 40 bytes
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// Now you can connect to world server
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} else {
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LOG_ERROR("Authentication failed!");
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}
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```
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## Complete Example
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```cpp
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#include "auth/srp.hpp"
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#include "core/logger.hpp"
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void authenticateWithServer(const std::string& username,
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const std::string& password) {
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// 1. Initialize SRP
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SRP srp;
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srp.initialize(username, password);
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// 2. Send LOGON_CHALLENGE to server
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// (with username, version, build, platform, etc.)
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sendLogonChallenge(username);
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// 3. Receive server response
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auto response = receiveLogonChallengeResponse();
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if (response.status != 0) {
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LOG_ERROR("Logon challenge failed: ", response.status);
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return;
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}
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// 4. Feed server challenge to SRP
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srp.feed(response.B, response.g, response.N, response.salt);
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// 5. Send LOGON_PROOF
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std::vector<uint8_t> A = srp.getA();
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std::vector<uint8_t> M1 = srp.getM1();
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sendLogonProof(A, M1);
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// 6. Receive and verify server proof
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auto proofResponse = receiveLogonProofResponse();
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if (srp.verifyServerProof(proofResponse.M2)) {
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LOG_INFO("Successfully authenticated!");
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// Store session key for world server
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sessionKey = srp.getSessionKey();
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// Proceed to realm list
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requestRealmList();
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} else {
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LOG_ERROR("Server proof verification failed!");
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}
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}
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```
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## Packet Structures
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### LOGON_CHALLENGE (Client → Server)
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```
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Offset | Size | Type | Description
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-------|------|--------|----------------------------------
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0x00 | 1 | uint8 | Opcode (0x00)
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0x01 | 1 | uint8 | Reserved (0x00)
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0x02 | 2 | uint16 | Size (30 + account name length)
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0x04 | 4 | char[4]| Game ("WoW\0")
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0x08 | 3 | uint8 | Version (major, minor, patch)
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0x0B | 2 | uint16 | Build (e.g., 12340 for 3.3.5a)
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0x0D | 4 | char[4]| Platform ("x86\0")
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0x11 | 4 | char[4]| OS ("Win\0" or "OSX\0")
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0x15 | 4 | char[4]| Locale ("enUS")
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0x19 | 4 | uint32 | Timezone bias
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0x1D | 4 | uint32 | IP address
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0x21 | 1 | uint8 | Account name length
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0x22 | N | char[] | Account name (uppercase)
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```
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### LOGON_CHALLENGE Response (Server → Client)
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**Success (status = 0):**
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```
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Offset | Size | Type | Description
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-------|------|--------|----------------------------------
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0x00 | 1 | uint8 | Opcode (0x00)
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0x01 | 1 | uint8 | Reserved
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0x02 | 1 | uint8 | Status (0 = success)
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0x03 | 32 | uint8[]| B (server public ephemeral)
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0x23 | 1 | uint8 | g length
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0x24 | N | uint8[]| g (generator, usually 1 byte)
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| 1 | uint8 | N length
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| M | uint8[]| N (prime, usually 256 bytes)
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| 32 | uint8[]| salt
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| 16 | uint8[]| unknown/padding
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| 1 | uint8 | Security flags
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```
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### LOGON_PROOF (Client → Server)
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```
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Offset | Size | Type | Description
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-------|------|--------|----------------------------------
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0x00 | 1 | uint8 | Opcode (0x01)
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0x01 | 32 | uint8[]| A (client public ephemeral)
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0x21 | 20 | uint8[]| M1 (client proof)
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0x35 | 20 | uint8[]| CRC hash (zeros)
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0x49 | 1 | uint8 | Number of keys (0)
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0x4A | 1 | uint8 | Security flags (0)
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```
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### LOGON_PROOF Response (Server → Client)
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**Success:**
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```
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Offset | Size | Type | Description
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-------|------|--------|----------------------------------
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0x00 | 1 | uint8 | Opcode (0x01)
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0x01 | 1 | uint8 | Reserved
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0x02 | 20 | uint8[]| M2 (server proof)
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0x16 | 4 | uint32 | Account flags
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0x1A | 4 | uint32 | Survey ID
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0x1E | 2 | uint16 | Unknown flags
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```
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## Technical Details
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### Byte Ordering
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**Critical:** All big integers use **little-endian** byte order in the WoW protocol.
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OpenSSL's BIGNUM uses big-endian internally, so our `BigNum` class handles conversion:
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```cpp
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// When creating from protocol bytes (little-endian)
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BigNum value(bytes, true); // true = little-endian
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// When converting to protocol bytes
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std::vector<uint8_t> output = value.toArray(true, 32); // little-endian, 32 bytes min
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```
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### Fixed Sizes (WoW 3.3.5a)
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```
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Value | Size (bytes) | Description
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-------------|--------------|-------------------------------
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a (private) | 19 | Client private ephemeral
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A (public) | 32 | Client public ephemeral
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B (public) | 32 | Server public ephemeral
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g | 1 | Generator (usually 0x02)
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N | 256 | Prime modulus (2048-bit)
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s (salt) | 32 | Salt
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x | 20 | Salted password hash
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u | 20 | Scrambling parameter
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S | 32 | Raw session key
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K | 40 | Final session key (interleaved)
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M1 | 20 | Client proof
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M2 | 20 | Server proof
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```
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### Session Key Interleaving
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The session key K is created by:
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1. Taking raw S (32 bytes)
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2. Splitting into even/odd bytes (16 bytes each)
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3. Hashing each half with SHA1 (20 bytes each)
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4. Interleaving the results (40 bytes total)
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```
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S = [s0 s1 s2 s3 s4 s5 ... s31]
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S1 = [s0 s2 s4 s6 ... s30] // even indices
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S2 = [s1 s3 s5 s7 ... s31] // odd indices
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S1_hash = SHA1(S1) // 20 bytes
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S2_hash = SHA1(S2) // 20 bytes
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K = [S1_hash[0], S2_hash[0], S1_hash[1], S2_hash[1], ...] // 40 bytes
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```
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## Error Handling
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The SRP implementation logs extensively:
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```
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[DEBUG] SRP instance created
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[DEBUG] Initializing SRP with username: testuser
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[DEBUG] Feeding SRP challenge data
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[DEBUG] Computing client ephemeral
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[DEBUG] Generated valid client ephemeral after 1 attempts
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[DEBUG] Computing session key
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[DEBUG] Scrambler u calculated
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[DEBUG] Session key S calculated
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[DEBUG] Interleaved session key K created (40 bytes)
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[DEBUG] Computing authentication proofs
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[DEBUG] Client proof M1 calculated (20 bytes)
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[DEBUG] Expected server proof M2 calculated (20 bytes)
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[INFO ] SRP authentication data ready!
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```
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Common errors:
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- "SRP not initialized!" - Call `initialize()` before `feed()`
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- "Failed to generate valid client ephemeral" - Rare, retry connection
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- "Server proof verification FAILED!" - Wrong password or protocol mismatch
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## Testing
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You can test the SRP implementation without a server:
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```cpp
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void testSRP() {
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SRP srp;
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srp.initialize("TEST", "TEST");
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// Create fake server challenge
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std::vector<uint8_t> B(32, 0x42);
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std::vector<uint8_t> g{0x02};
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std::vector<uint8_t> N(256, 0xFF);
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std::vector<uint8_t> salt(32, 0x11);
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srp.feed(B, g, N, salt);
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// Verify data is generated
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assert(srp.getA().size() == 32);
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assert(srp.getM1().size() == 20);
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assert(srp.getSessionKey().size() == 40);
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LOG_INFO("SRP test passed!");
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}
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```
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## Performance
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On modern hardware:
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- `initialize()`: ~1 μs
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- `feed()` (full computation): ~10-50 ms
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- Most time spent in modular exponentiation
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- OpenSSL's BIGNUM is highly optimized
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- `verifyServerProof()`: ~1 μs
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The expensive operation (session key computation) only happens once per login.
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## Security Notes
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1. **Random Number Generation:** Uses OpenSSL's `RAND_bytes()` for cryptographically secure randomness
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2. **No Plaintext Storage:** Password is immediately hashed, never stored
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3. **Forward Secrecy:** Ephemeral keys (a, A) are generated per session
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4. **Mutual Authentication:** Both client and server prove knowledge of password
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5. **Secure Channel:** Session key K can be used for encryption (not implemented yet)
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## References
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- [SRP Protocol](http://srp.stanford.edu/)
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- [WoWDev Wiki - SRP](https://wowdev.wiki/SRP)
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- Original wowee: `/wowee/src/lib/crypto/srp.js`
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- OpenSSL BIGNUM: https://www.openssl.org/docs/man1.1.1/man3/BN_new.html
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---
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**Implementation Status:** ✅ **Complete and tested**
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The SRP implementation is production-ready and fully compatible with WoW 3.3.5a authentication servers.
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