# Bitcoin Script ASM Format Freddie Honohan () ## Abstract This proposal introduces a standardised method of dealing with the ASM representation of Bitcoin Script across the ecosystem language libraries (Py-SDK, TS-SDK, Go-SDK, Teranode etc). ## Motivation The purpose of this proposal is to provide a generalised standard in order for deterministic translation of Bitcoin Script to and from ASM for cross-language compatibility. Currently, different implementations may produce inconsistent ASM representations for the same script. For example, the boolean value `false` might be rendered as `OP_0`, `OP_FALSE` depending on the library used. This lack of standardisation creates interoperability issues when scripts are shared across different tools and platforms. ## Specification 1. It is important that ASM format scripts operate correctly regardless of where they were produced or processed. 2. The Hexadecimal and Binary representations are defined in BRC-14. 3. Since ASM format is primarily used for human-readability, op-codes with multiple representations like the boolean pair `[OP_0, OP_1]` are to be represented as their english full-name counterpart e.g. `[OP_FALSE, OP_TRUE]` **Example:** ``` Hex: 0x00 0x51 ASM: OP_FALSE OP_TRUE Not: OP_0 OP_1 ``` 4. Other discrepancies were found and documented [here](https://docs.google.com/spreadsheets/d/106aSWsOeNayzXOU9tRmRIvSu2Cz21YZQ5uCrwMZg1WU/) and rules are set out below to deal with them. ## Implementation 1. The logic dealing with Bitcoin Script ASM is to be standardised across libraries and languages as described hereunder. 2. Op-Codes with several names must be parsed into the correct hex/binary byte despite the chosen ASM format name. **Example Input Parsing:** ```javascript // All of these should parse to 0x00 parseASM("OP_0") // ✓ valid parseASM("OP_FALSE") // ✓ valid // Both should output the same hex parseASM("OP_0") === parseASM("OP_FALSE") // true ``` 3. However op-codes with several names must be output into the most human-readable format (e.g. `OP_0` will always output as `OP_FALSE`). **Example Output Serialization:** ```javascript // Input hex, always outputs human-readable form toASM(0x00) // "OP_FALSE" (not "OP_0") toASM(0x51) // "OP_TRUE" (not "OP_1") ``` 4. Full Op-Code to Hex Table With Statuses | Index | Word | Hex | Legacy | Chronicles | | ----- | ----------------------- | --------- | -------- | ---------- | | 0 | OP\_FALSE | 0x00 | ✅ | ✅ | | 1-75 | OP\_PUSHDATA | 0x01-0x4b | ✅ | ✅ | | 76 | OP\_PUSHDATA1 | 0x4c | ✅ | ✅ | | 77 | OP\_PUSHDATA2 | 0x4d | ✅ | ✅ | | 78 | OP\_PUSHDATA4 | 0x4e | ✅ | ✅ | | 79 | OP\_1NEGATE | 0x4f | ✅ | ✅ | | 80 | OP\_RESERVED | 0x50 | Reserved | Reserved | | 81 | OP\_TRUE | 0x51 | ✅ | ✅ | | 82 | OP\_2 | 0x52 | ✅ | ✅ | | 83 | OP\_3 | 0x53 | ✅ | ✅ | | 84 | OP\_4 | 0x54 | ✅ | ✅ | | 85 | OP\_5 | 0x55 | ✅ | ✅ | | 86 | OP\_6 | 0x56 | ✅ | ✅ | | 87 | OP\_7 | 0x57 | ✅ | ✅ | | 88 | OP\_8 | 0x58 | ✅ | ✅ | | 89 | OP\_9 | 0x59 | ✅ | ✅ | | 90 | OP\_10 | 0x5a | ✅ | ✅ | | 91 | OP\_11 | 0x5b | ✅ | ✅ | | 92 | OP\_12 | 0x5c | ✅ | ✅ | | 93 | OP\_13 | 0x5d | ✅ | ✅ | | 94 | OP\_14 | 0x5e | ✅ | ✅ | | 95 | OP\_15 | 0x5f | ✅ | ✅ | | 96 | OP\_16 | 0x60 | ✅ | ✅ | | 97 | OP\_NOP | 0x61 | ✅ | ✅ | | 98 | OP\_VER | 0x62 | ❌ | ✅ | | 99 | OP\_IF | 0x63 | ✅ | ✅ | | 100 | OP\_NOTIF | 0x64 | ✅ | ✅ | | 101 | OP\_VERIF | 0x65 | ❌ | ✅ | | 102 | OP\_VERNOTIF | 0x66 | ❌ | ✅ | | 103 | OP\_ELSE | 0x67 | ✅ | ✅ | | 104 | OP\_ENDIF | 0x68 | ✅ | ✅ | | 105 | OP\_VERIFY | 0x69 | ✅ | ✅ | | 106 | OP\_RETURN | 0x6a | ✅ | ✅ | | 107 | OP\_TOALTSTACK | 0x6b | ✅ | ✅ | | 108 | OP\_FROMALTSTACK | 0x6c | ✅ | ✅ | | 109 | OP\_2DROP | 0x6d | ✅ | ✅ | | 110 | OP\_2DUP | 0x6e | ✅ | ✅ | | 111 | OP\_3DUP | 0x6f | ✅ | ✅ | | 112 | OP\_2OVER | 0x70 | ✅ | ✅ | | 113 | OP\_2ROT | 0x71 | ✅ | ✅ | | 114 | OP\_2SWAP | 0x72 | ✅ | ✅ | | 115 | OP\_IFDUP | 0x73 | ✅ | ✅ | | 116 | OP\_DEPTH | 0x74 | ✅ | ✅ | | 117 | OP\_DROP | 0x75 | ✅ | ✅ | | 118 | OP\_DUP | 0x76 | ✅ | ✅ | | 119 | OP\_NIP | 0x77 | ✅ | ✅ | | 120 | OP\_OVER | 0x78 | ✅ | ✅ | | 121 | OP\_PICK | 0x79 | ✅ | ✅ | | 122 | OP\_ROLL | 0x7a | ✅ | ✅ | | 123 | OP\_ROT | 0x7b | ✅ | ✅ | | 124 | OP\_SWAP | 0x7c | ✅ | ✅ | | 125 | OP\_TUCK | 0x7d | ✅ | ✅ | | 126 | OP\_CAT | 0x7e | ✅ | ✅ | | 127 | OP\_SPLIT | 0x7f | ✅ | ✅ | | 128 | OP\_NUM2BIN | 0x80 | ✅ | ✅ | | 129 | OP\_BIN2NUM | 0x81 | ✅ | ✅ | | 130 | OP\_SIZE | 0x82 | ✅ | ✅ | | 131 | OP\_INVERT | 0x83 | ✅ | ✅ | | 132 | OP\_AND | 0x84 | ✅ | ✅ | | 133 | OP\_OR | 0x85 | ✅ | ✅ | | 134 | OP\_XOR | 0x86 | ✅ | ✅ | | 135 | OP\_EQUAL | 0x87 | ✅ | ✅ | | 136 | OP\_EQUALVERIFY | 0x88 | ✅ | ✅ | | 137 | OP\_RESERVED1 | 0x89 | Reserved | Reserved | | 138 | OP\_RESERVED2 | 0x8a | Reserved | Reserved | | 139 | OP\_1ADD | 0x8b | ✅ | ✅ | | 140 | OP\_1SUB | 0x8c | ✅ | ✅ | | 141 | OP\_2MUL | 0x8d | ❌ | ✅ | | 142 | OP\_2DIV | 0x8e | ❌ | ✅ | | 143 | OP\_NEGATE | 0x8f | ✅ | ✅ | | 144 | OP\_ABS | 0x90 | ✅ | ✅ | | 145 | OP\_NOT | 0x91 | ✅ | ✅ | | 146 | OP\_0NOTEQUAL | 0x92 | ✅ | ✅ | | 147 | OP\_ADD | 0x93 | ✅ | ✅ | | 148 | OP\_SUB | 0x94 | ✅ | ✅ | | 149 | OP\_MUL | 0x95 | ✅ | ✅ | | 150 | OP\_DIV | 0x96 | ✅ | ✅ | | 151 | OP\_MOD | 0x97 | ✅ | ✅ | | 152 | OP\_LSHIFT | 0x98 | ✅ | ✅ | | 153 | OP\_RSHIFT | 0x99 | ✅ | ✅ | | 154 | OP\_BOOLAND | 0x9a | ✅ | ✅ | | 155 | OP\_BOOLOR | 0x9b | ✅ | ✅ | | 156 | OP\_NUMEQUAL | 0x9c | ✅ | ✅ | | 157 | OP\_NUMEQUALVERIFY | 0x9d | ✅ | ✅ | | 158 | OP\_NUMNOTEQUAL | 0x9e | ✅ | ✅ | | 159 | OP\_LESSTHAN | 0x9f | ✅ | ✅ | | 160 | OP\_GREATERTHAN | 0xa0 | ✅ | ✅ | | 161 | OP\_LESSTHANOREQUAL | 0xa1 | ✅ | ✅ | | 162 | OP\_GREATERTHANOREQUAL | 0xa2 | ✅ | ✅ | | 163 | OP\_MIN | 0xa3 | ✅ | ✅ | | 164 | OP\_MAX | 0xa4 | ✅ | ✅ | | 165 | OP\_WITHIN | 0xa5 | ✅ | ✅ | | 166 | OP\_RIPEMD160 | 0xa6 | ✅ | ✅ | | 167 | OP\_SHA1 | 0xa7 | ✅ | ✅ | | 168 | OP\_SHA256 | 0xa8 | ✅ | ✅ | | 169 | OP\_HASH160 | 0xa9 | ✅ | ✅ | | 170 | OP\_HASH256 | 0xaa | ✅ | ✅ | | 171 | OP\_CODESEPARATOR | 0xab | ✅ | ✅ | | 172 | OP\_CHECKSIG | 0xac | ✅ | ✅ | | 173 | OP\_CHECKSIGVERIFY | 0xad | ✅ | ✅ | | 174 | OP\_CHECKMULTISIG | 0xae | ✅ | ✅ | | 175 | OP\_CHECKMULTISIGVERIFY | 0xaf | ✅ | ✅ | | 176 | OP\_NOP1 | 0xb0 | ✅ | ✅ | | 177 | OP\_NOP2 | 0xb1 | ✅ | ✅ | | 178 | OP\_NOP3 | 0xb2 | ✅ | ✅ | | 179 | OP\_SUBSTR | 0xb3 | ❌ | ✅ | | 180 | OP\_LEFT | 0xb4 | ❌ | ✅ | | 181 | OP\_RIGHT | 0xb5 | ❌ | ✅ | | 182 | OP\_NOP4 | 0xb6 | ✅ | ✅ | | 183 | OP\_NOP5 | 0xb7 | ✅ | ✅ | | 184 | OP\_NOP6 | 0xb8 | ✅ | ✅ | | 185 | OP\_NOP7 | 0xb9 | ✅ | ✅ | | 186 | OP\_NOP8 | 0xba | ✅ | ✅ | | 187 | OP\_NOP9 | 0xbb | ✅ | ✅ | | 188 | OP\_NOP10 | 0xbc | ✅ | ✅ | | 253 | OP\_PUBKEYHASH | 0xfd | Pseudo | Pseudo | | 254 | OP\_PUBKEY | 0xfe | Pseudo | Pseudo | | 255 | OP\_INVALIDOPCODE | 0xff | Invalid | Invalid | ## References * [BRC-14](https://bsv.brc.dev/scripts/0014): Bitcoin Script Binary and Hex Formats - Ty Everett ()