CoTA NFT Protocol Extension

There are four predefined smt_type enum for NFT operations.

type name	1st byte	2nd byte	description
cota-NFT-define	0x81 (NFT)	0x00	NFT issuance definition
cota-NFT-hold	0x81 (NFT)	0x01	current hold NFT
cota-NFT-withdrawal	0x81 (NFT)	0x02	NFT withdrawal record
cota-NFT-claim	0x81 (NFT)	0x03	NFT claim record

Here are the detailed k-v definitions.

# cota-NFT-define data structure
key:
    smt_type:  uint16         # type bytes for cota-NFT-define big endian
    token_id:  Byte[20]       # hash(inputs[0].out_point + first_cota_index)[0..20]
    reserved:  Byte[10]    
value:
    total:     uint32         # 0 for unlimited
    issued:    uint32
    configure: Byte[1]
    reserved:  Byte[22]
    ending:    0xFF           # in case all-zero value

# cota-NFT-hold data structure
key:
    smt_type:  uint16         # type byte for cota-NFT-hold
    token_id:  Byte[20]
    index_id:  uint32
    reserved:  Byte[6]      
value:
    configure: Byte[1]
    state:     Byte[1]
    characteristic: Byte[20]  # user-defined data
    reserved:  Byte[9]
    ending:    0xFF           # in case all-zero value

# cota-NFT-withdraw data structure
key:  
    smt_type:  uint16         # type byte for cota-NFT-withdraw
    token_id:   Byte[20]
    index_id:  uint32
    reserved:  Byte[6]
value:
blake2b_hash of {
    configure: Byte[1]
    state:     Byte[1]
    characteristic: Byte[20]      # user-defined data
    to_lock:   lock_script
    out_point: OutPoint[12..36]   # Outpoint of previous input cell with SMT
}

# cota-NFT-claim data structure
key: 
blake2b_hash of {
    smt_type:  uint16             # type byte for cota-NFT-claim
    token_id:  Byte[20]
    index_id:  uint32    
    out_point: OutPoint[12..36]   # Outpoint field recorded in the proof
value:
    0x00...00 for nonclaimed
    0xFF...FF for claimed

Where token_id (also written as cota_id in the early designs) is an UUID for all fungible and non-fungible tokens. Its value is set according to the token definition transaction data.

token_id = hash(tx.inputs[0].out_point | tx.outputs.get_first(cota_type).index)[0..20]