Scripting Transactions
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The document summarizes a class on scripting and transactions in cryptocurrency. It discusses how Bitcoin core code has evolved over time to interpret scripts for locking and unlocking transactions. Examples are provided of common script patterns used prior to 2010, including pay-to-pubkey-hash and an important bug discovered that could allow stealing outputs. More advanced scripting options are also mentioned, such as checkmultisig.
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Vout: ([]btcjson.Vout) (len=2 cap=4) {
(btcjson.Vout) {
Value: (float64) 229,
N: (uint32) 0,
ScriptPubKey: (btcjson.ScriptPubKeyResult) {
Asm: (string) (len=85) "OP_DUP OP_HASH160
d6980467719f0e93e9742b6389e09117b6b630a3 OP_EQUALVERIFY OP_CHECKSIG",
Hex: (string) (len=50) "76a914d6980467719f0e93e9742b6389e09117b6b630a388ac",
ReqSigs: (int32) 1,
Type: (string) (len=10) "pubkeyhash",
Addresses: ([]string) (len=1 cap=4) {
(string) (len=34) "PsVSrUSQf72X6GWFQXJPxR7WSAPVRb1gWx"
}
}
},](https://image.slidesharecdn.com/class15-post-151020175535-lva1-app6891/85/Scripting-Transactions-10-320.jpg)
![10
OP_DUP
OP_HASH160
d6980467719f0e93e9742b6389e09117b6b630a3
OP_EQUALVERIFY
OP_CHECKSIG
OP_DUP [x] Duplicates the top stack item
OP_HASH160 [x] Replaces top of stack with RIPEMD160(SHA256([top]))
OP_EQUALVERIFY [x1] [x2] If top two items are equal, outputs True;
otherwise, marks transaction as Invalid.
OP_CHECKSIG [pubkey] [sig] Checks that E_pubkey(sig)([entire transaction])
LockingScript](https://image.slidesharecdn.com/class15-post-151020175535-lva1-app6891/85/Scripting-Transactions-11-320.jpg)
![“Pay-to-Script-Hash”
15
OP_HASH160
[20-byte hash]
OP_EQUAL
LockingScript](https://image.slidesharecdn.com/class15-post-151020175535-lva1-app6891/85/Scripting-Transactions-16-320.jpg)
![More Powerful Scripts
24
OP_CHECKMULTISIG [x] [sig]k [pub key]k
valid := 0
for each signature [1, k]:
if checksig(sigk, pubk): valid += 1
if valid >= x: 1
else: 0](https://image.slidesharecdn.com/class15-post-151020175535-lva1-app6891/85/Scripting-Transactions-25-320.jpg)
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Scripting Transactions
- 1. Class 15: Scripting Transactions Cryptocurrency Cabal cs4501 Fall 2015 David Evans and Samee Zahur University of Virginia
- 2. Plan for Today Scripting Transactions Review/PS2 1 Reminders Extra office hours (see notes) Midterm Wednesday (in class) Problem Set 3
- 8. 7 https://github.com/bitcoin/bitcoin/blob/41e6e4caba9899ce7c165b0784461c55c867ee24/src/script/interpreter.cpp#L524 Version 0.1 Project idea: look at how bitcoin core code has evolved over time Latest
- 9. 8
- 10. 9 Vout: ([]btcjson.Vout) (len=2 cap=4) { (btcjson.Vout) { Value: (float64) 229, N: (uint32) 0, ScriptPubKey: (btcjson.ScriptPubKeyResult) { Asm: (string) (len=85) "OP_DUP OP_HASH160 d6980467719f0e93e9742b6389e09117b6b630a3 OP_EQUALVERIFY OP_CHECKSIG", Hex: (string) (len=50) "76a914d6980467719f0e93e9742b6389e09117b6b630a388ac", ReqSigs: (int32) 1, Type: (string) (len=10) "pubkeyhash", Addresses: ([]string) (len=1 cap=4) { (string) (len=34) "PsVSrUSQf72X6GWFQXJPxR7WSAPVRb1gWx" } } },
- 11. 10 OP_DUP OP_HASH160 d6980467719f0e93e9742b6389e09117b6b630a3 OP_EQUALVERIFY OP_CHECKSIG OP_DUP [x] Duplicates the top stack item OP_HASH160 [x] Replaces top of stack with RIPEMD160(SHA256([top])) OP_EQUALVERIFY [x1] [x2] If top two items are equal, outputs True; otherwise, marks transaction as Invalid. OP_CHECKSIG [pubkey] [sig] Checks that E_pubkey(sig)([entire transaction]) LockingScript
- 12. 11
- 17. Unlocking/Locking (pre-2010) 16 OP_DUP OP_HASH160 <bitcoin address (hash of public key)> OP_EQUALVERIFY OP_CHECKSIG LockingScript <signature> <public key> UnlockingScript
- 18. OP_RETURN 17 Original meaning: terminate script execution, leaving stack unchanged. https://github.com/bitcoin/bitcoin/blob/v0.1.5/script.cpp#L170
- 19. Steal any output! 18 OP_DUP OP_HASH160 <bitcoin address (hash of public key)> OP_EQUALVERIFY OP_CHECKSIG LockingScriptUnlockingScript
- 20. Steal any output! 19 OP_DUP OP_HASH160 <bitcoin address (hash of public key)> OP_EQUALVERIFY OP_CHECKSIG LockingScriptUnlockingScript This is the by far biggest bug in bitcoin (discovered so far!).
- 21. OP_RETURN (fixed July 2010) 20 https://github.com/btcsuite/btcd/blob/c153596542b3d87dd774c29aa5be5117ac01a234/txscript/opcode.go#L1239 https://github.com/bitcoin/bitcoin/blob/41e6e4caba9899ce7c165b0784461c55c867ee24/src/script/interpreter.cpp#L397
- 22. Actual Scripts in Bitcoin 21
- 23. 22 (first 290,000 blocks, through 2014-03-11)
- 25. More Powerful Scripts 24 OP_CHECKMULTISIG [x] [sig]k [pub key]k valid := 0 for each signature [1, k]: if checksig(sigk, pubk): valid += 1 if valid >= x: 1 else: 0
- 27. 26 https://github.com/SabaEskandarian/CryptocurrencyProject Saba Eskandarian’s project last semester
- 28. 27
- 29. Charge Wednesday: Midterm Upcoming office hours: Today: 5-6:30 (Ori, Rice 442) Tomorrow: 2-3:30pm (Dave, Rice 507) Tomorrow: 3:30-4:30pm (Samee, Rice 442) 28