diff --git a/modules/sdk-core/src/account-lib/mpc/tss/ecdsa/ecdsa.ts b/modules/sdk-core/src/account-lib/mpc/tss/ecdsa/ecdsa.ts
index 3476eb2d9f..74cc5f9854 100644
--- a/modules/sdk-core/src/account-lib/mpc/tss/ecdsa/ecdsa.ts
+++ b/modules/sdk-core/src/account-lib/mpc/tss/ecdsa/ecdsa.ts
@@ -1357,10 +1357,13 @@ export default class Ecdsa {
    * @param {OShare} oShare private omicron share of current participant
    * @param {DShare} dShare delta share received from the other participant
    * @param {Hash} hash hashing algorithm implementing Node`s standard crypto hash interface
-   * @param shouldHash if true, we hash the provided buffer before signing
+   * @param shouldHash if true, we hash the provided buffer before signing. If false, M must be exactly 32 bytes (a hash).
    * @returns {VAShare}
    */
   sign(M: Buffer, oShare: OShare, dShare: DShare, hash?: Hash, shouldHash = true): VAShare {
+    if (!shouldHash && M.length !== 32) {
+      throw new Error(`When shouldHash=false, message must be exactly 32 bytes (a hash), but got ${M.length} bytes`);
+    }
     const m = shouldHash ? (hash || createHash('sha256')).update(M).digest() : M;
 
     const delta = Ecdsa.curve.scalarAdd(hexToBigInt(oShare.delta), hexToBigInt(dShare.delta));
@@ -1560,10 +1563,15 @@ export default class Ecdsa {
    * @param {Buffer} message
    * @param {Signature } signature
    * @param {Hash} hash hashing algorithm implementing Node`s standard crypto hash interface
-   * @param {boolean} shouldHash if true, we hash the provided buffer before verifying
+   * @param {boolean} shouldHash if true, we hash the provided buffer before verifying. If false, message must be exactly 32 bytes (a hash).
    * @returns {boolean} True if signature is valid; False otherwise
    */
   verify(message: Buffer, signature: Signature, hash?: Hash, shouldHash = true): boolean {
+    if (!shouldHash && message.length !== 32) {
+      throw new Error(
+        `When shouldHash=false, message must be exactly 32 bytes (a hash), but got ${message.length} bytes`
+      );
+    }
     const messageToVerify = shouldHash ? (hash || createHash('sha256')).update(message).digest() : message;
     return Ecdsa.curve.verify(
       messageToVerify,
diff --git a/modules/sdk-core/test/unit/account-lib/mpc/tss/ecdsa/ecdsa.ts b/modules/sdk-core/test/unit/account-lib/mpc/tss/ecdsa/ecdsa.ts
index 6ff3183b4b..964b4a7511 100644
--- a/modules/sdk-core/test/unit/account-lib/mpc/tss/ecdsa/ecdsa.ts
+++ b/modules/sdk-core/test/unit/account-lib/mpc/tss/ecdsa/ecdsa.ts
@@ -26,6 +26,32 @@ describe('ecdsa tss', function () {
 
   let signCombine1: SignCombineRT, signCombine2: SignCombineRT;
 
+  function signAndVerify(message: Buffer, shouldHash = true): boolean {
+    const [sign1, sign2] = [
+      ecdsa.sign(message, signCombine1.oShare, signCombine2.dShare, undefined, shouldHash),
+      ecdsa.sign(message, signCombine2.oShare, signCombine1.dShare, undefined, shouldHash),
+    ];
+
+    const [signWithProofs1, signWithProofs2] = [
+      ecdsa.generateVAProofs(message, sign1),
+      ecdsa.generateVAProofs(message, sign2),
+    ];
+
+    const [UT1, UT2] = [
+      ecdsa.verifyVAShares(signWithProofs1, [signWithProofs2]),
+      ecdsa.verifyVAShares(signWithProofs2, [signWithProofs1]),
+    ];
+
+    const [publicUTShares_1, publicUTShares_2] = [UT1, UT2];
+    const [signature1, signature2] = [
+      ecdsa.verifyUTShares(UT1, [publicUTShares_2]),
+      ecdsa.verifyUTShares(UT2, [publicUTShares_1]),
+    ];
+
+    const signature = ecdsa.constructSignature([signature1, signature2]);
+    return ecdsa.verify(message, signature, undefined, shouldHash);
+  }
+
   before('generate key and sign phase 1 to 4', async function () {
     // In some execution environments (e.g. CI), generateNtilde below may take longer at times.
     this.timeout('40s');
@@ -158,8 +184,6 @@ describe('ecdsa tss', function () {
   });
 
   it('sign phase 5 should succeed', async function () {
-    // TODO(HSM-129): There is a bug signing unhashed message (although this deviates from DSA spec) if the message is a little long.
-    //       Some discrepancy between Ecdsa.sign and secp256k1.recoverPublicKey on handling the message input.
     const message = Buffer.from('GG18 PHASE 5');
 
     // Starting phase 5
@@ -271,4 +295,41 @@ describe('ecdsa tss', function () {
     (() => ecdsa.verifyUTShares(UT1, [publicUTShares_2])).should.throw('Sum of all U_i does not match sum of all T_i');
     (() => ecdsa.verifyUTShares(UT2, [publicUTShares_1])).should.throw('Sum of all U_i does not match sum of all T_i');
   });
+
+  describe('shouldHash parameter', function () {
+    it('should validate message length when shouldHash=false', function () {
+      const hash32 = Buffer.alloc(32, 0x01);
+      const shortMessage = Buffer.from('Short');
+      const longMessage = Buffer.from('This is a longer message that exceeds 32 bytes in length');
+
+      (() => ecdsa.sign(hash32, signCombine1.oShare, signCombine2.dShare, undefined, false)).should.not.throw();
+
+      (() => ecdsa.sign(shortMessage, signCombine1.oShare, signCombine2.dShare, undefined, false)).should.throw(
+        /must be exactly 32 bytes/
+      );
+      (() => ecdsa.sign(longMessage, signCombine1.oShare, signCombine2.dShare, undefined, false)).should.throw(
+        /must be exactly 32 bytes/
+      );
+
+      const dummySig = { r: '00', s: '00', recid: 0, y: signCombine1.oShare.y };
+      (() => ecdsa.verify(shortMessage, dummySig, undefined, false)).should.throw(/must be exactly 32 bytes/);
+      (() => ecdsa.verify(longMessage, dummySig, undefined, false)).should.throw(/must be exactly 32 bytes/);
+    });
+
+    it('should work correctly with shouldHash=false when message is 32 bytes', async function () {
+      const { createHash } = require('crypto');
+      const message = Buffer.from('Any message');
+      const messageHash = createHash('sha256').update(message).digest();
+
+      signAndVerify(messageHash, false).should.equal(true);
+    });
+
+    it('should work correctly with shouldHash=true for any message length', async function () {
+      const shortMessage = Buffer.from('Short message');
+      const longMessage = Buffer.from('This is a longer message that exceeds 32 bytes in length');
+
+      signAndVerify(shortMessage, true).should.equal(true);
+      signAndVerify(longMessage, true).should.equal(true);
+    });
+  });
 });