Gavin_Andresen - 2011-12-13 16:05:42

Here's how to figure it out from the Satoshi client code:

The IMPLEMENT_SERIALIZE macro is used to both store transactions on disk and to serialize them into a byte-array that can be hashed.

For class CTransaction, that looks like:

Code:

IMPLEMENT_SERIALIZE
   (
   READWRITE(this->nVersion);
   nVersion = this->nVersion;
   READWRITE(vin);
   READWRITE(vout);
   READWRITE(nLockTime);
   )

READWRITE is a wrapper that is overloaded to Do The Right Thing for all the types bitcoin deals with; for complex types like CTxOut, IMPLEMENT_SERIALIZE is (essentially) called recursively.

Expand out all of the types and, assuming I didn't screw up (always an iffy assumption), it looks like a CTransaction is serialized as:

Code:

nVersion
vin.size (vectors are serialized as a compressed count immediately followed by their contents)
vin[].prevout (vin->prevout->hash followed immediately by vin->prevout->n, as 36 bytes)
vin[].scriptSig (CScripts are serialized as a vector of bytes)
vin[].nSequence
... repeated for each vin
vout.size
vout[].nValue
vout[].scriptPubKey
... repeated for each vout
nLockTime

String all those bytes together, SHA256 them twice, and you should get the transaction hash for the merkle chain.

Gavin Andresen - 2011-12-13 16:05:42