3.4 KiB
Cryptography
ISAAC
ISAAC is a cryptographically-secure pseudorandom number generator. By combining its output with addition/subtraction, the client uses it as a stream cipher to encrypt the opcodes of packets.
It was implemented to break packet injection bots, such as AutoRune. While using ISAAC in this manner only provides confidentiality, and not authenticity or integrity, if the opcodes are tampered with the packet lengths will no longer be in sync between the client and server. This causes one or both of the endpoints to read garbage opcodes, though the garbage opcodes may happen to match valid packets for a while. Eventually, one or both endpoints will detect an invalid packet and close the connection.
RSA
RSA is an asymmetric encryption and signature algorithm. The client uses it to protect the user's password and the session's symmetric key during the login process.
In later revisions, the JS5 master index is signed with Jagex's private key. This change was made around the time the native libraries were moved into the cache, ensuring that Jagex's code-signed applet could not be used to run arbitrary native code if an attacker tampers with the JS5 connection. This change was probably required by Jagex's certificate authority.
Jagex used a 512-bit RSA key when build 550 was released, and due to the size of the output buffer in the client, the maximum key size is 1,008 bits. Both of these sizes are considered insecure by modern standards, and Jagex's 512-bit private key was factored in 2016.
Textbook RSA is used, rather than a secure padding scheme, which leads to several weaknesses.
SHA-1
SHA-1 is a cryptographic hash function. It is used to verify the integrity of the game's code. SHA-1 is no longer secure.
XTEA
XTEA is a symmetric block cipher. It is primarily used to encrypt location files in the cache, reportedly to prevent bots from performing path-finding across the entire map - the server only provides keys for a location file when the player is within or adjacent to it.
It is used in Electronic codebook (ECB) mode. ECB is theoretically insecure, however, as the location files are compressed before encryption it is difficult to make use of this insecurity in practice.
The location files do not contain padding, and therefore the last 0-7 bytes are leaked. This has no practical impact as they only contain a portion of the gzip or bzip2 trailer.
It is also used (in ECB mode, but with padding) to encrypt the player's email address in the create account packet, with the symmetric key encrypted with RSA. XTEA is used as email addresses may sometimes be too long to be encrypted directly by Jagex's 512-bit RSA key.
Whirlpool
Whirlpool is a cryptographic hash function. It is not used in build 550, however, it is included here for completeness as it is supported by OpenRS2's cache library. It is used to verify the integrity of native libraries stored in the cache.