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Randomize change transaction output index.

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Based on a diff created by @dajohi.
This commit is contained in:
Josh Rickmar 2014-06-12 22:28:30 -05:00
parent e4c0fc81dd
commit e7b1fc7e9f
1 changed files with 7 additions and 3 deletions
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10
createtx.go
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@ -20,6 +20,7 @@ import (
"bytes" "bytes"
"errors" "errors"
"fmt" "fmt"
badrand "math/rand"
"sort" "sort"
"sync" "sync"
"time" "time"
@ -204,9 +205,6 @@ func (a *Account) txToPairs(pairs map[string]btcutil.Amount,
// Check if there are leftover unspent outputs, and return coins back to // Check if there are leftover unspent outputs, and return coins back to
// a new address we own. // a new address we own.
//
// TODO: change needs to be inserted into a random txout index, or else
// this is a privacy risk.
change := btcin - amt - fee change := btcin - amt - fee
if change > 0 { if change > 0 {
// Get a new change address if one has not already been found. // Get a new change address if one has not already been found.
@ -226,6 +224,12 @@ func (a *Account) txToPairs(pairs map[string]btcutil.Amount,
return nil, fmt.Errorf("cannot create txout script: %s", err) return nil, fmt.Errorf("cannot create txout script: %s", err)
} }
msgtx.AddTxOut(btcwire.NewTxOut(int64(change), pkScript)) msgtx.AddTxOut(btcwire.NewTxOut(int64(change), pkScript))
// Randomize index of the change output.
rng := badrand.New(badrand.NewSource(time.Now().UnixNano()))
r := rng.Int31n(int32(len(msgtx.TxOut))) // random index
c := len(msgtx.TxOut) - 1 // change index
msgtx.TxOut[r], msgtx.TxOut[c] = msgtx.TxOut[c], msgtx.TxOut[r]
} }
// Selected unspent outputs become new transaction's inputs. // Selected unspent outputs become new transaction's inputs.