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Hash Pre-Image Sequence Commitment

Basic Pre-Image Sequence

Alice commits C into an output such that she can reveal R_N = HASH( ... HASH( C )). We combine that to create transactions with dynamic lock times.

1 Bit Commitment

OP_HASH256

<COMMITMENT_HASH>

OP_SWAP

OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        24
        OP_CHECKSEQUENCEVERIFY                               
OP_ENDIF
OP_HASH256
OP_EQUALVERIFY

Spendable with:

1 <COMMITMENT_PREIMAGE>

OR

0 <HASH256(COMMITMENT_PREIMAGE)>

4 Bit Commitment

COMMITMENT = HASH(HASH(HASH(HASH(PREIMAGE))))

OP_HASH256
<COMMITMENT_HASH>

OP_SWAP


OP_ROT
OP_IF	
        OP_EQUALVERIFY                        
        24
        OP_CHECKSEQUENCEVERIFY                               
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF	
        OP_EQUALVERIFY                        
        18
        OP_CHECKSEQUENCEVERIFY                               
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF	
        OP_EQUALVERIFY                        
        12
        OP_CHECKSEQUENCEVERIFY                               
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF	
        OP_EQUALVERIFY                        
        6
        OP_CHECKSEQUENCEVERIFY                               
OP_ENDIF

Example Input

Hashed three times, spendable after 12 blocks.

0 0 1 0 <HASH(HASH(HASH256(PREIMAGE)))>

Hashed two times, spendable after 6 blocks.

0 0 0 1 <HASH(HASH256(PREIMAGE))>

2 Parties

Alice and Bob create an output in the Blockchain such that they can change its timelock afterwards.

Using two such time lock commitments in a payment channel with Alice and Bob, they can always execute their most recent state in a single transaction.


OP_HASH256



<COMMITMENT_1>
OP_SWAP



OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        24
        OP_CODESEPARATOR                                                       
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        18
        OP_CODESEPARATOR                                                       
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        12
        OP_CODESEPARATOR                                                       
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        6
        OP_CODESEPARATOR                                                       
OP_ENDIF

   
   
OP_CHECKSEQUENCEVERIFY
OP_DROP






<COMMITMENT_2>
OP_SWAP



OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        24
        OP_CODESEPARATOR                                                       
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        18
        OP_CODESEPARATOR                                                       
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        12
        OP_CODESEPARATOR                                                       
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        6
        OP_CODESEPARATOR                                                       
OP_ENDIF

   
   
OP_CHECKSEQUENCEVERIFY
OP_DROP








2
<ALICE KEY>
<BOB KEY>
2
OP_CHECKMULTISIG

The OP_CODESEPARATOR guarantee signatures bind to pre-images. To trigger the N-th case Alice can not use any of Bob's signatures except for his N-th.

View in Script Editor

Limitations

  • 7 bit per party = 14 bit commitment + 2-of-2 signature

Multiple Hash Functions

Use multiple hash functions to encode more states.

<COMMITMENT_HASH>

OP_SWAP


OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        24
        OP_CHECKSEQUENCEVERIFY                               
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        18
        OP_CHECKSEQUENCEVERIFY                               
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        12
        OP_CHECKSEQUENCEVERIFY                               
OP_ENDIF
OP_HASH256


OP_ROT
OP_IF   
        OP_EQUALVERIFY                        
        6
        OP_CHECKSEQUENCEVERIFY                               
OP_ENDIF

References