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 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

• 0x00-0x03 Personality value
• 0x04-0x05 Unknown
• 0x06-0x07 Checksum

Block A

• 0x08-0x09 Species ID
• 0x0A-0x0B Held Item
• 0x0C-0x0D OT ID
• 0x0E-0x0F OT Secret ID
• 0x10-0x13 Experience points
• 0x14 Friendship/Egg Steps to Hatch
• 0x15 Ability
• 0x16 Markings
• 0x17 Country of Origin
• 0x18-0x1D Effort values
• 0x1E-0x23 Contest stats
• 0x24-0x27 Ribbons

Block B

• 0x28-0x2F Moveset
• 0x30-0x33 Move PP
• 0x34-0x37 Move PP Ups
• 0x38-0x3B Individual values
• 0x3C-0x3F Ribbons 2
• 0x40 Gender
• 0x41-0x47 Unknown

Block C

• 0x48-0x5D Nickname
• 0x5E Unknown
• 0x5F Hometown
• 0x60-0x62 Contests
• 0x63-0x67 Unknown

Block D

• 0x68-0x77 OT Name
• 0x78-0x7A Date Egg Received
• 0x7B-0x7D Date Met
• 0x7E-0x7F Egg Location
• 0x80-0x81 Met At Location
• 0x82 Pokérus
• 0x83 Poké Ball
• 0x84 Met At Level
• 0x85 Encounter Type
• 0x86-0x87 Unknown