Validate mnemonic checksum

packages/primitives/src/mnemonic.ts

@@ -74,7 +74,10 @@ export class Mnemonic {
    *
    * @returns Instance of Mnemonic.
    */
-  public static fromEntropy(entropy: Uint8Array, wordList: Array<string> = bip39WordListEnglish) {
+  public static fromEntropy(
+    entropy: Uint8Array,
+    wordList: Array<string> = bip39WordListEnglish,
+  ) {
     const mnemonic = encodeBip39MnemonicNonStandard(entropy, wordList);
 
     if (typeof mnemonic === 'string') {
@@ -167,6 +170,18 @@ export class Mnemonic {
       );
     }
 
+    // Ensure the checksum is correct by attempting to decode the mnemonic.
+    // NOTE: LibAuth doesn't currently expose a convenient function to check this by itself.
+    const decodeResult = decodeBip39MnemonicNonStandard(
+      mnemonicRaw.words.join(' '),
+      wordList,
+    );
+
+    // NOTE: The above function will return a string if there is an error.
+    if (typeof decodeResult === 'string') {
+      throw new Error(decodeResult);
+    }
+
     return new this(mnemonicRaw);
   }
 

packages/primitives/tests/mnemonic.spec.ts

@@ -327,4 +327,23 @@ describe('Fail cases', () => {
       ]);
     }).toThrow();
   });
+
+  it('fromWord should fail if checksum is invalid', () => {
+    expect(() => {
+      // Invalid word "fnord".
+      Mnemonic.fromWords([
+        'abandon',
+        'abandon',
+        'abandon',
+        'abandon',
+        'abandon',
+        'abandon',
+        'abandon',
+        'abandon',
+        'abandon',
+        'abandon',
+        'banana',
+      ]);
+    }).toThrow();
+  });
 });