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76 lines
3.4 KiB
76 lines
3.4 KiB
4 years ago
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# Cryptography
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## ISAAC
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[ISAAC][isaac] is a cryptographically-secure pseudorandom number generator. By
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combining its output with addition/subtraction, the client uses it as a stream
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cipher to encrypt the opcodes of packets.
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It was implemented to break packet injection bots, such as AutoRune. While
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using ISAAC in this manner only provides confidentiality, and not authenticity
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or integrity, if the opcodes are tampered with the packet lengths will no
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longer be in sync between the client and server. This causes one or both of the
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endpoints to read garbage opcodes, though the garbage opcodes may happen to
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match valid packets for a while. Eventually, one or both endpoints will detect
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an invalid packet and close the connection.
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## RSA
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[RSA][rsa] is an asymmetric encryption and signature algorithm. The client uses
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it to protect the user's password and the session's symmetric key during the
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login process.
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In later revisions, the JS5 master index is signed with Jagex's private key.
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This change was made around the time the native libraries were moved into the
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cache, ensuring that Jagex's code-signed applet could not be used to run
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arbitrary native code if an attacker tampers with the JS5 connection. This
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change was probably required by Jagex's certificate authority.
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Jagex used a 512-bit RSA key when build 550 was released, and due to the size
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of the output buffer in the client, the maximum key size is 1,008 bits. Both of
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these sizes are considered insecure by modern standards, and Jagex's 512-bit
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private key was factored in 2016.
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Textbook RSA is used, rather than a secure padding scheme, which leads to
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[several weaknesses][textbook-rsa].
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## SHA-1
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[SHA-1][sha1] is a cryptographic hash function. It is used to verify the
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integrity of the game's code. SHA-1 is no longer secure.
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## XTEA
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[XTEA][xtea] is a symmetric block cipher. It is primarily used to encrypt
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location files in the cache, reportedly to prevent bots from performing
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path-finding across the entire map - the server only provides keys for a
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location file when the player is within or adjacent to it.
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It is used in [Electronic codebook (ECB)][ecb] mode. ECB is theoretically
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insecure, however, as the location files are compressed before encryption it is
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difficult to make use of this insecurity in practice.
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The location files do not contain padding, and therefore the last 0-7 bytes are
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leaked. This has no practical impact as they only contain a portion of the gzip
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or bzip2 trailer.
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It is also used (in ECB mode, but with padding) to encrypt the player's email
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address in the create account packet, with the symmetric key encrypted with RSA.
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XTEA is used as email addresses may sometimes be too long to be encrypted
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directly by Jagex's 512-bit RSA key.
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## Whirlpool
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[Whirlpool][whirlpool] is a cryptographic hash function. It is not used in
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build 550, however, it is included here for completeness as it is supported by
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OpenRS2's cache library. It is used to verify the integrity of native libraries
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stored in the cache.
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[ecb]: https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_codebook_(ECB)
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[isaac]: https://burtleburtle.net/bob/rand/isaacafa.html
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[rsa]: https://en.wikipedia.org/wiki/RSA_(cryptosystem)
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[sha1]: https://en.wikipedia.org/wiki/SHA-1
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[textbook-rsa]: https://en.wikipedia.org/wiki/RSA_(cryptosystem)#Attacks_against_plain_RSA
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[whirlpool]: https://en.wikipedia.org/wiki/Whirlpool_(hash_function)
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[xtea]: https://en.wikipedia.org/wiki/XTEA
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