fix(algo): surface rekey and block blind signing of rekeyed txs

modules/sdk-coin-algo/src/algo.ts

@@ -29,6 +29,7 @@ import {
   TransactionExplanation,
   TransactionRecipient,
   TransactionType,
+  InvalidTransactionError,
   UnexpectedAddressError,
   VerifyAddressOptions,
   VerifyTransactionOptions,
@@ -74,6 +75,7 @@ export interface VerifyAlgoAddressOptions extends VerifyAddressOptions {
 export interface AlgoTransactionExplanation extends TransactionExplanation {
   memo?: string;
   type?: string | number;
+  reKeyTo?: string;
   voteKey?: string;
   selectionKey?: string;
   voteFirst?: number;
@@ -91,6 +93,13 @@ export interface TransactionOperation {
 export interface SignTransactionOptions extends BaseSignTransactionOptions {
   txPrebuild: TransactionPrebuild;
   prv: string;
+  /**
+   * Explicit opt-in required to sign a transaction that sets `reKeyTo`: the exact rekey
+   * address that was shown to and approved by the operator. A rekey hands spending
+   * authority of the account to another address, so signing throws if the decoded
+   * transaction rekeys to any other address.
+   */
+  allowReKeyTo?: string;
 }
 
 export interface TransactionPrebuild {
@@ -357,7 +366,7 @@ export class Algo extends BaseCoin {
    * @param params
    */
   async explainTransaction(params: ExplainTransactionOptions): Promise<AlgoTransactionExplanation | undefined> {
-    const txHex = params.txHex || (params.halfSigned && params.halfSigned.txHex);
+    const txHex = (params.halfSigned && params.halfSigned.txHex) || params.txHex;
     if (!txHex || !params.feeInfo) {
       throw new Error('missing explain tx parameters');
     }
@@ -412,6 +421,13 @@ export class Algo extends BaseCoin {
         operations,
       };
 
+      // A rekey silently reassigns spending authority of the account, so it must never
+      // be hidden from the explanation shown for approval.
+      if (txJson.reKeyTo) {
+        displayOrder.push('reKeyTo');
+        explanationResult.reKeyTo = txJson.reKeyTo;
+      }
+
       if (txJson.tokenId) {
         explanationResult.tokenId = txJson.tokenId;
       }
@@ -432,7 +448,7 @@ export class Algo extends BaseCoin {
         'voteKeyDilution',
       ];
 
-      return {
+      const explanationResult: AlgoTransactionExplanation = {
         displayOrder,
         id: txJson.id,
         outputAmount: '0',
@@ -448,6 +464,14 @@ export class Algo extends BaseCoin {
         voteLast: txJson.voteLast,
         voteKeyDilution: txJson.voteKeyDilution,
       };
+
+      // A keyreg transaction can also carry a rekey; surface it like in the send case.
+      if (txJson.reKeyTo) {
+        displayOrder.push('reKeyTo');
+        explanationResult.reKeyTo = txJson.reKeyTo;
+      }
+
+      return explanationResult;
     }
   }
 
@@ -550,6 +574,20 @@ export class Algo extends BaseCoin {
    */
   async signTransaction(params: SignTransactionOptions): Promise<SignedTransaction> {
     const { txHex, signers, prv, isHalfSigned, numberSigners } = this.verifySignTransactionParams(params);
+    // A rekey reassigns spending authority of the account; refuse to sign it unless the
+    // caller passes the exact rekey address the operator approved. A bare opt-in would
+    // also approve a different rekey target hidden in the bytes being signed.
+    // Note: this guards Algo.signTransaction only; other signing entry points (e.g.
+    // callers driving TransactionBuilder.sign directly) are not covered.
+    const { txn } = Utils.decodeAlgoTxn(txHex);
+    if (txn.reKeyTo) {
+      const reKeyAddress = algosdk.encodeAddress(txn.reKeyTo.publicKey);
+      if (params.allowReKeyTo !== reKeyAddress) {
+        throw new InvalidTransactionError(
+          `transaction rekeys the account to ${reKeyAddress}: refusing to sign unless the rekey is confirmed intentional (pass allowReKeyTo with the approved rekey address)`
+        );
+      }
+    }
     const factory = this.getBuilder();
     const txBuilder = factory.from(txHex);
     txBuilder.numberOfRequiredSigners(numberSigners);

modules/sdk-coin-algo/src/lib/ifaces.ts

@@ -20,6 +20,7 @@ export interface TxData {
   genesisID: string;
   genesisHash: string | Buffer;
   closeRemainderTo?: string;
+  reKeyTo?: string;
   nonParticipation?: boolean;
   txType?: string;
   tokenName?: string;

modules/sdk-coin-algo/src/lib/keyRegistrationBuilder.ts

@@ -143,7 +143,8 @@ export class KeyRegistrationBuilder extends TransactionBuilder {
       undefined, // voteFirst param
       undefined, // voteLast param
       undefined, // voteKeyDilution param
-      this.suggestedParams
+      this.suggestedParams,
+      this._reKeyTo
     );
   }
 
@@ -157,7 +158,7 @@ export class KeyRegistrationBuilder extends TransactionBuilder {
       this._voteLast,
       this._voteKeyDilution,
       this.suggestedParams,
-      undefined, // reKeyTo param
+      this._reKeyTo,
       undefined, // nonParticipation param
       this._stateProofKey
     );

modules/sdk-coin-algo/src/lib/transaction.ts

@@ -252,6 +252,9 @@ export class Transaction extends BaseTransaction {
     if (this._algoTransaction.closeRemainderTo) {
       result.closeRemainderTo = algosdk.encodeAddress(this._algoTransaction.closeRemainderTo.publicKey);
     }
+    if (this._algoTransaction.reKeyTo) {
+      result.reKeyTo = algosdk.encodeAddress(this._algoTransaction.reKeyTo.publicKey);
+    }
     if (this.type === TransactionType.Send) {
       result.to = algosdk.encodeAddress(this._algoTransaction.to.publicKey);
       result.amount = this._algoTransaction.amount.toString();

modules/sdk-coin-algo/test/unit/algo.ts

@@ -233,6 +233,52 @@ describe('ALGO:', function () {
       explain.outputs[0].amount.should.equal(amount.toString());
       explain.outputs[0].address.should.equal(destination);
     });
+
+    it('should surface the rekey target when explaining a transfer transaction that rekeys the account', async function () {
+      const sender = AlgoResources.accounts.account1.address;
+      const destination = AlgoResources.accounts.account2.address;
+      const rekeyAddress = AlgoResources.accounts.account3.address;
+      const txBuilder = buildBaseTransferTransaction({ sender, destination, amount: 10000 });
+      txBuilder.reKeyTo({ address: rekeyAddress });
+      const unsignedTransaction = await txBuilder.build();
+      const unsignedHex = Buffer.from(unsignedTransaction.toBroadcastFormat()).toString('hex');
+      const explain = await basecoin.explainTransaction({
+        txHex: unsignedHex,
+        feeInfo: { fee: '1000' },
+      });
+      explain.reKeyTo.should.equal(rekeyAddress);
+      explain.displayOrder.should.containEql('reKeyTo');
+      explain.outputs[0].address.should.equal(destination);
+    });
+
+    it('should explain the halfSigned transaction when both txHex and halfSigned txHex are provided', async function () {
+      const sender = AlgoResources.accounts.account1.address;
+      const destination = AlgoResources.accounts.account2.address;
+      const rekeyAddress = AlgoResources.accounts.account3.address;
+
+      // plain unsigned payment without a rekey, used as the misleading txHex
+      const plainHex = Buffer.from(
+        (await buildBaseTransferTransaction({ sender, destination, amount: 10000 }).build()).toBroadcastFormat()
+      ).toString('hex');
+
+      // half-signed payment that rekeys the account, used as the halfSigned txHex
+      const rekeyedBuilder = buildBaseTransferTransaction({ sender, destination, amount: 10000 });
+      rekeyedBuilder.reKeyTo({ address: rekeyAddress });
+      rekeyedBuilder.numberOfSigners(2);
+      rekeyedBuilder.setSigners([AlgoResources.accounts.account1.address, AlgoResources.accounts.account3.address]);
+      rekeyedBuilder.sign({ key: AlgoResources.accounts.account1.prvKey });
+      const halfSignedHex = Buffer.from((await rekeyedBuilder.build()).toBroadcastFormat()).toString('hex');
+
+      // signTransaction signs the halfSigned hex when both are present, so the
+      // explanation must come from the same bytes, not from txHex
+      const explain = await basecoin.explainTransaction({
+        txHex: plainHex,
+        halfSigned: { txHex: halfSignedHex },
+        feeInfo: { fee: '1000' },
+      });
+      explain.reKeyTo.should.equal(rekeyAddress);
+      explain.displayOrder.should.containEql('reKeyTo');
+    });
   });
 
   describe('Asset Transfer Builder: ', () => {
@@ -349,6 +395,23 @@ describe('ALGO:', function () {
       explain.outputs[0].address.should.equal(destination);
       explain.tokenId.should.equal(1);
     });
+
+    it('should surface the rekey target when explaining an asset transfer transaction that rekeys the account', async function () {
+      const sender = AlgoResources.accounts.account1.address;
+      const destination = AlgoResources.accounts.account2.address;
+      const rekeyAddress = AlgoResources.accounts.account3.address;
+      const txBuilder = buildBaseAssetTransferTransaction({ sender, destination, amount: 10000, tokenId: 1 });
+      txBuilder.reKeyTo({ address: rekeyAddress });
+      const unsignedTransaction = await txBuilder.build();
+      const unsignedHex = Buffer.from(unsignedTransaction.toBroadcastFormat()).toString('hex');
+      const explain = await basecoin.explainTransaction({
+        txHex: unsignedHex,
+        feeInfo: { fee: '1000' },
+      });
+      explain.reKeyTo.should.equal(rekeyAddress);
+      explain.displayOrder.should.containEql('reKeyTo');
+      explain.outputs[0].address.should.equal(destination);
+    });
   });
 
   describe('Wallet Init Builder: ', () => {
@@ -538,6 +601,21 @@ describe('ALGO:', function () {
       explain.voteLast.should.equal(100);
       explain.voteKeyDilution.should.equal(9);
     });
+
+    it('should surface the rekey target when explaining a keyreg transaction that rekeys the account', async function () {
+      const sender = AlgoResources.accounts.account1;
+      const rekeyAddress = AlgoResources.accounts.account3.address;
+      const txBuilder = buildBaseKeyRegTransaction({ sender });
+      txBuilder.reKeyTo({ address: rekeyAddress });
+      const unsignedTransaction = await txBuilder.build();
+      const unsignedHex = Buffer.from(unsignedTransaction.toBroadcastFormat()).toString('hex');
+      const explain = await basecoin.explainTransaction({
+        txHex: unsignedHex,
+        feeInfo: { fee: '1000' },
+      });
+      explain.reKeyTo.should.equal(rekeyAddress);
+      explain.displayOrder.should.containEql('reKeyTo');
+    });
   });
   describe('Sign transaction', () => {
     it('should sign transaction', async function () {
@@ -648,6 +726,99 @@ describe('ALGO:', function () {
       });
       signed.txHex.should.equal(AlgoResources.rawTx.transfer.multisig);
     });
+
+    it('should refuse to sign a transaction that rekeys the account', async function () {
+      const factory = new TransactionBuilderFactory(coins.get('algo'));
+      const txBuilder = factory
+        .getTransferBuilder()
+        .sender({ address: AlgoResources.accounts.account1.address })
+        .to({ address: AlgoResources.accounts.account2.address })
+        .amount(10000)
+        .isFlatFee(true)
+        .fee({ fee: '1000' })
+        .firstRound(1)
+        .lastRound(100)
+        .testnet();
+      txBuilder.reKeyTo({ address: AlgoResources.accounts.account3.address });
+      const unsignedTx = await txBuilder.build();
+      const unsignedHex = Buffer.from(unsignedTx.toBroadcastFormat()).toString('hex');
+
+      await basecoin
+        .signTransaction({
+          txPrebuild: {
+            txHex: unsignedHex,
+            keys: [AlgoResources.accounts.account1.pubKey.toString('hex')],
+            addressVersion: 1,
+          },
+          prv: AlgoResources.accounts.account1.prvKey,
+        })
+        .should.be.rejectedWith(
+          new RegExp(
+            `transaction rekeys the account to ${AlgoResources.accounts.account3.address}: refusing to sign unless the rekey is confirmed intentional`
+          )
+        );
+    });
+
+    it('should sign a transaction that rekeys the account when the rekey is explicitly allowed', async function () {
+      const factory = new TransactionBuilderFactory(coins.get('algo'));
+      const txBuilder = factory
+        .getTransferBuilder()
+        .sender({ address: AlgoResources.accounts.account1.address })
+        .to({ address: AlgoResources.accounts.account2.address })
+        .amount(10000)
+        .isFlatFee(true)
+        .fee({ fee: '1000' })
+        .firstRound(1)
+        .lastRound(100)
+        .testnet();
+      txBuilder.reKeyTo({ address: AlgoResources.accounts.account3.address });
+      const unsignedTx = await txBuilder.build();
+      const unsignedHex = Buffer.from(unsignedTx.toBroadcastFormat()).toString('hex');
+
+      const signed = await basecoin.signTransaction({
+        txPrebuild: {
+          txHex: unsignedHex,
+          keys: [AlgoResources.accounts.account1.pubKey.toString('hex')],
+          addressVersion: 1,
+        },
+        prv: AlgoResources.accounts.account1.prvKey,
+        allowReKeyTo: AlgoResources.accounts.account3.address,
+      });
+      assert.strictEqual(typeof signed.txHex, 'string');
+    });
+
+    it('should refuse to sign a rekeyed transaction when the approved rekey address does not match', async function () {
+      const factory = new TransactionBuilderFactory(coins.get('algo'));
+      const txBuilder = factory
+        .getTransferBuilder()
+        .sender({ address: AlgoResources.accounts.account1.address })
+        .to({ address: AlgoResources.accounts.account2.address })
+        .amount(10000)
+        .isFlatFee(true)
+        .fee({ fee: '1000' })
+        .firstRound(1)
+        .lastRound(100)
+        .testnet();
+      txBuilder.reKeyTo({ address: AlgoResources.accounts.account3.address });
+      const unsignedTx = await txBuilder.build();
+      const unsignedHex = Buffer.from(unsignedTx.toBroadcastFormat()).toString('hex');
+
+      await basecoin
+        .signTransaction({
+          txPrebuild: {
+            txHex: unsignedHex,
+            keys: [AlgoResources.accounts.account1.pubKey.toString('hex')],
+            addressVersion: 1,
+          },
+          prv: AlgoResources.accounts.account1.prvKey,
+          allowReKeyTo: AlgoResources.accounts.account2.address,
+        })
+        .should.be.rejectedWith(
+          new RegExp(
+            `transaction rekeys the account to ${AlgoResources.accounts.account3.address}: refusing to sign unless the rekey is confirmed intentional`
+          )
+        );
+    });
   });
 
   describe('Sign message', () => {