Unit EOLib.Encrypt

Description

Uses

Classes, Interfaces, Objects and Records

Functions and Procedures

Types

Constants

Variables

Description

Utilities to handle EO data encryption.

Overview

Functions and Procedures

procedure Interleave(var Data: TArray<Byte>);

procedure Deinterleave(var Data: TArray<Byte>);

procedure FlipMsb(var Data: TArray<Byte>);

procedure SwapMultiples(var Data: TArray<Byte>; Multiple: Cardinal);

function ServerVerificationHash(Challenge: Cardinal): Integer;

Description

Functions and Procedures

procedure Interleave(var Data: TArray<Byte>);

Interleaves a sequence of bytes. When encrypting EO data, bytes are "woven" into each other.
Used when encrypting packets and data files.

Example:

[0, 1, 2, 3, 4, 5] → [0, 5, 1, 4, 2, 3]

This is an in-place operation.

Parameters

Data: The data to interleave

procedure Deinterleave(var Data: TArray<Byte>);

Deinterleaves a sequence of bytes. This is the reverse of Interleave.
Used when decrypting packets and data files.

Example:

[0, 1, 2, 3, 4, 5] → [0, 2, 4, 5, 3, 1]

This is an in-place operation.

Parameters

Data: The data to deinterleave

procedure FlipMsb(var Data: TArray<Byte>);

Flips the most significant bits of each byte in a sequence of bytes. (Values 0 and 128 are not flipped.)
Used when encrypting and decrypting packets.

Example:

[0, 1, 127, 128, 129, 254, 255] → [0, 129, 255, 128, 1, 126, 127]

This is an in-place operation.

Parameters

Data: The data to flip most significant bits on

procedure SwapMultiples(var Data: TArray<Byte>; Multiple: Cardinal);

Swaps the order of contiguous bytes in a sequence of bytes that are divisible by a given multiple value.
Used when encrypting and decrypting packets and data files.

Example:

Multiple := 3
[10, 21, 27] → [10, 27, 21]

This is an in-place operation.

Parameters

Data: The data to swap bytes in
Multiple: The multiple value

function ServerVerificationHash(Challenge: Cardinal): Integer;

This hash function is how the game client checks that it's communicating with a genuine server during connection initialization.

The client sends an integer value to the server in the INIT_INIT client packet, where it is referred to as the Challenge.
The server hashes the value and sends the hash back in the INIT_INIT server packet.
The client hashes the value and compares it to the hash sent by the server.
If the hashes don't match, the client drops the connection.

Warning: Oversized challenges may result in negative hash values, which cannot be represented properly in the EO protocol.

Parameters

Challenge: The challenge value sent by the client. Should be no larger than 11,092,110

Returns

The hashed challenge value

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