Pokémon data structure (Generation IV): Difference between revisions

Boxed Pokémon in the games Diamond and Pearl are stored in a 136-byte structure. All unencrypted values are stored in little-endian format. The game encrypts the data when it is stored into save data. In-party Pokémon have additional values appended to them to hold calculated stats. The information below describes the boxed Pokémon data format.

Checksum

The checksum serves two purposes:

1. It validates the data after decryption, and
2. It serves as the encryption key for the data.

The checksum is calculated in three steps:

1. Split the unencrypted data from offsets 0x08 to 0x87 into two-byte words,
2. Take the sum of the words, and
3. Truncate the sum to sixteen bits.

Block Shuffling

The 128 bytes of Pokémon data are split into four 32-byte blocks for shuffling. The blocks are shuffled according to a shift value derived from the personality value. Give the personality value pv, the expression yielding the shift value is:

((pv >> 0xD) & 0x1F) % 24

To shuffle the blocks, take the four blocks of unencrypted data to be A, B, C, and D. The blocks shall be rearranged in the encrypted data according to this table:

Encryption

The encryption uses the pseudorandom number generator (PRNG), a linear congruential generator. Elements of the PRNG can be described with the recursive function:

X[n+1] = (0x41C64E6D * X[n] + 0x6073) % 0xFFFFFFFF

To decrypt the data, given a function rand() which returns the upper 16 bits of consecutive results of the above given function:

1. Seed the PRNG with the checksum (let X[n] be the checksum),
2. Sequentially, for each 2-byte word Y from 0x08 to 0x87, apply the transformation: unencryptedByte = Y xor rand()
3. Un-shuffle the blocks using the block shuffling algorithm above.

Unencrypted bytes

Block A

Block B

Block C

Block D