When an original World of Warcraft client (1.2 through to 3.3.5) authenticates with the server the client will send a hash of some local game files. This post details how the client calculates the hash for World of Warcraft 1.12 and provides replication values in order to test your own implementation.

Background

The server sends a checksum salt in CMD_AUTH_LOGON_CHALLENGE_Server in the field just after the SRP6 salt. The client sends the final hash in CMD_AUTH_LOGON_PROOF_Client in the field just after the client proof.

The client does not require the server to make this calculation like it does for the SRP6 algorithm and malicious clients can just fake the proof, so there’s no real security benefits to implementing this check.

The integrity check is different for login and reconnection. The integrity check is not platform specific, but the specific files and contents of those files are platform and version specific.

This guide is specifically for 1.12, although it will probably work on other versions as well.

Implementation details for login

The implementation is a HMAC-SHA1 of game files together with the server provided checksum salt, and then a SHA1 of the resulting HMAC along with the client public key. The implementation is not different for Mac/Windows, it only differs in the files that are checked.

Generic

This describes a function that can be used for both Windows and Mac without any modifications. The algorithm is the same as the platform specific versions, but all the checked files are just concatenated into a single slice to make the function generic.

• checksum_salt is sent by the server in CMD_AUTH_LOGON_CHALLENGE_Server in the field just after the SRP6 salt.
• all_files is all platform specific files concatenated together. See the platform specific versions for which specific files.
• client_public_key is the client public key provided by the client.
• + is array concatenation.

Calculating the integrity hash in pseudo code would look like:

function integrity_check_generic
    argument all_files: array of an arbitrary amount of bytes
    argument checksum_salt: array of 16 bytes
    argument client_public_key: array of 32 bytes
    returns array of 20 bytes

    checksum_hmac = HmacSha1(checksum_salt)
    checksum_hmac.update(all_files)

    checksum = checksum_hmac.finalize()

    return SHA1(client_public_key + checksum)

Implementations

• Rust (wow_srp)
• C++ (Ember)

Verification values

• generic_regression

Windows

The windows integrity calculation uses the generic version, but it specifically enumerates the files required for Windows.

• wow_exe, the bytes of the WoW.exe file.
• fmod_dll, the bytes of the fmod.dll file.
• ijl15_dll, the bytes of the ijl15.dll file.
• dbghelp_dll, the bytes of the dbghelp.dll file.
• unicows_dll, the bytes of the unicows.dll file.
• checksum_salt is sent by the server in CMD_AUTH_LOGON_CHALLENGE_Server in the field just after the SRP6 salt.
• client_public_key is the client public key provided by the client.
• + is array concatenation.

Calculating the integrity hash in pseudo code would look like:

function integrity_check_windows
    argument wow_exe: array of an arbitrary amount of bytes
    argument fmod_dll: array of an arbitrary amount of bytes
    argument ijl15_dll: array of an arbitrary amount of bytes
    argument dbghelp_dll: array of an arbitrary amount of bytes
    argument unicows_dll: array of an arbitrary amount of bytes
    argument checksum_salt: array of 16 bytes
    argument client_public_key: array of 32 bytes
    returns array of 20 bytes

    all_files = wow_exe + fmod_dll + ijl15_dll + dbghelp_dll + unicows_dll

    return integrity_check_generic(all_files, checksum_salt, client_public_key)

Verification values

• windows_regression

Mac

The windows integrity calculation uses the generic version, but it specifically enumerates the files required for Windows.

• world_of_warcraft, the bytes of the MacOS/World of Warcraft file.
• info_plist, the bytes of the Info.plist file.
• objects_xib, the bytes of the Resources/Main.nib/objects.xib file.
• wow_icns, the bytes of the Resources/wow.icns file.
• pkg_info, the bytes of the PkgInfo file.
• checksum_salt is sent by the server CMD_AUTH_LOGON_CHALLENGE_Server in the field just after the SRP6 salt.
• client_public_key is the client public key provided by the client.
• + is array concatenation.

Calculating the integrity hash in pseudo code would look like:

function integrity_check_windows
    argument world_of_warcraft: array of an arbitrary amount of bytes
    argument info_plist: array of an arbitrary amount of bytes
    argument objects_xib: array of an arbitrary amount of bytes
    argument wow_icns: array of an arbitrary amount of bytes
    argument pkg_info: array of an arbitrary amount of bytes
    argument checksum_salt: array of 16 bytes
    argument client_public_key: array of 32 bytes
    returns array of 20 bytes

    all_files = world_of_warcraft + info_plist + objects_xib + ow_icns + pkg_info

    return integrity_check_generic(all_files, checksum_salt, client_public_key)

Verification values

• mac_regression

Implementation details for reconnect

The reconnection integrity check does away with any local files and simply gets the SHA1 of the provided salt along with a zero buffer. This is likely to save on resources since it would be very unlikely for the files to change in between login and reconnecting.

• checksum_salt is sent by the server CMD_AUTH_RECONNECT_CHALLENGE_Server in the field just after the SRP6 salt.
• + is array concatenation.

Calculating the reconnect integrity hash in pseudo code would look like:

function integrity_check_reconnect
    argument checksum_salt: array of an arbitrary amount of bytes

    # Array of 20 bytes, filled with zero
    all_zero = [0; 20]

    return SHA1(checksum_salt + all_zero)

Verification values

• reconnect_regression

Implementations

• Rust (wow_srp)
• C++ (Ember)