Pokémon data structure (Generation IV)

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 result 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

• 00-03 Personality value
• 04-05 Unknown
• 06-07 Checksum

Block A

• 08-09 Species ID
• 0A-0B Held Item
• 0C-0D OT ID
• 0E-0F OT Secret ID
• 10-13 Experience points
• 14 Friendship/Egg Steps to Hatch
• 15 Ability
• 16 Markings
• 17 Country of Origin
• 18-1D Effort values
• 1E-23 Contest stats
• 24-27 Ribbons

Block B

• 28-2F Moveset
• 30-33 Move PP
• 34-37 Move PP Ups
• 38-3B Individual values
• 3C-3F Ribbons 2
• 40 Gender
• 41-47 Unknown

Block C

• 48-5D Nickname
• 5E Unknown
• 5F Hometown
• 60-62 Contests
• 63-67 Unknown

Block D

• 68-77 OT Name
• 78-7A Date Egg Received
• 7B-7D Date Met
• 7E-7F Egg Location
• 80-81 Met At Location
• 82 Pokérus
• 83 Poké Ball
• 84 Met At Level
• 85 Encounter Type
• 86-87 Unknown