Add low R signing to TransactionBuilder

src/transaction_builder.js

@@ -29,6 +29,7 @@ class TransactionBuilder {
         this.__INPUTS = [];
         this.__TX = new transaction_1.Transaction();
         this.__TX.version = 2;
+        this.__USE_LOW_R = false;
     }
     static fromTransaction(transaction, network) {
         const txb = new TransactionBuilder(network);
@@ -53,6 +54,14 @@ class TransactionBuilder {
         });
         return txb;
     }
+    setLowR(setting) {
+        typeforce(typeforce.maybe(typeforce.Boolean), setting);
+        if (setting === undefined) {
+            setting = true;
+        }
+        this.__USE_LOW_R = setting;
+        return setting;
+    }
     setLockTime(locktime) {
         typeforce(types.UInt32, locktime);
         // if any signatures exist, throw
@@ -159,7 +168,7 @@ class TransactionBuilder {
             if (ourPubKey.length !== 33 && input.hasWitness) {
                 throw new Error('BIP143 rejects uncompressed public keys in P2WPKH or P2WSH');
             }
-            const signature = keyPair.sign(signatureHash);
+            const signature = keyPair.sign(signatureHash, this.__USE_LOW_R);
             input.signatures[i] = bscript.signature.encode(signature, hashType);
             return true;
         });

test/transaction_builder.js

@@ -338,6 +338,25 @@ describe('TransactionBuilder', () => {
       assert.strictEqual(txb.build().toHex(), '0100000001ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff010000006a47304402205f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f02205f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f5f0121031b84c5567b126440995d3ed5aaba0565d71e1834604819ff9c17f5e9d5dd078fffffffff01a0860100000000001976a914000000000000000000000000000000000000000088ac00000000')
     })
 
+    it('supports low R signature signing', () => {
+      let txb = new TransactionBuilder()
+      txb.setVersion(1)
+      txb.addInput('ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff', 1)
+      txb.addOutput('1111111111111111111114oLvT2', 100000)
+      txb.sign(0, keyPair)
+      // high R
+      assert.strictEqual(txb.build().toHex(), '0100000001ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff010000006b483045022100b872677f35c9c14ad9c41d83649fb049250f32574e0b2547d67e209ed14ff05d022059b36ad058be54e887a1a311d5c393cb4941f6b93a0b090845ec67094de8972b01210279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798ffffffff01a0860100000000001976a914000000000000000000000000000000000000000088ac00000000')
+
+      txb = new TransactionBuilder()
+      txb.setVersion(1)
+      txb.addInput('ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff', 1)
+      txb.addOutput('1111111111111111111114oLvT2', 100000)
+      txb.setLowR()
+      txb.sign(0, keyPair)
+      // low R
+      assert.strictEqual(txb.build().toHex(), '0100000001ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff010000006a473044022012a601efa8756ebe83e9ac7a7db061c3147e3b49d8be67685799fe51a4c8c62f02204d568d301d5ce14af390d566d4fd50e7b8ee48e71ec67786c029e721194dae3601210279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798ffffffff01a0860100000000001976a914000000000000000000000000000000000000000088ac00000000')
+    })
+
     fixtures.invalid.sign.forEach(f => {
       it('throws ' + f.exception + (f.description ? ' (' + f.description + ')' : ''), () => {
         const txb = construct(f, true)

ts_src/transaction_builder.ts

@@ -94,6 +94,7 @@ export class TransactionBuilder {
   private __PREV_TX_SET: { [index: string]: boolean };
   private __INPUTS: TxbInput[];
   private __TX: Transaction;
+  private __USE_LOW_R: boolean;
 
   // WARNING: maximumFeeRate is __NOT__ to be relied on,
   //          it's just another potential safety mechanism (safety in-depth)
@@ -105,6 +106,16 @@ export class TransactionBuilder {
     this.__INPUTS = [];
     this.__TX = new Transaction();
     this.__TX.version = 2;
+    this.__USE_LOW_R = false;
+  }
+
+  setLowR(setting?: boolean): boolean {
+    typeforce(typeforce.maybe(typeforce.Boolean), setting);
+    if (setting === undefined) {
+      setting = true;
+    }
+    this.__USE_LOW_R = setting;
+    return setting;
   }
 
   setLockTime(locktime: number): void {
@@ -266,7 +277,7 @@ export class TransactionBuilder {
         );
       }
 
-      const signature = keyPair.sign(signatureHash);
+      const signature = keyPair.sign(signatureHash, this.__USE_LOW_R);
       input.signatures![i] = bscript.signature.encode(signature, hashType!);
       return true;
     });

types/transaction_builder.d.ts

@@ -9,7 +9,9 @@ export declare class TransactionBuilder {
     private __PREV_TX_SET;
     private __INPUTS;
     private __TX;
+    private __USE_LOW_R;
     constructor(network?: Network, maximumFeeRate?: number);
+    setLowR(setting?: boolean): boolean;
     setLockTime(locktime: number): void;
     setVersion(version: number): void;
     addInput(txHash: Buffer | string | Transaction, vout: number, sequence?: number, prevOutScript?: Buffer): number;