fix: replace salt with info

xmtp · Mar 12, 2024 · a0e3ecd · a0e3ecd
1 parent 47d63da
commit a0e3ecd
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Showing 3 changed files with 28 additions and 17 deletions.
diff --git a/src/crypto/encryption.ts b/src/crypto/encryption.ts
@@ -3,6 +3,7 @@ import Ciphertext, { AESGCMNonceSize, KDFSaltSize } from './Ciphertext'
 import crypto from './crypto'
 
 const hkdfNoInfo = new Uint8Array().buffer
+const hkdfNoSalt = new Uint8Array().buffer
 
 // This is a variation of https://github.com/paulmillr/noble-secp256k1/blob/main/index.ts#L1378-L1388
 // that uses `digest('SHA-256', bytes)` instead of `digest('SHA-256', bytes.buffer)`
@@ -86,13 +87,13 @@ async function hkdf(secret: Uint8Array, salt: Uint8Array): Promise<CryptoKey> {
 
 export async function hkdfHmacKey(
   secret: Uint8Array,
-  salt: Uint8Array
+  info: Uint8Array
 ): Promise<CryptoKey> {
   const key = await crypto.subtle.importKey('raw', secret, 'HKDF', false, [
     'deriveKey',
   ])
   return crypto.subtle.deriveKey(
-    { name: 'HKDF', hash: 'SHA-256', salt, info: hkdfNoInfo },
+    { name: 'HKDF', hash: 'SHA-256', salt: hkdfNoSalt, info },
     key,
     { name: 'HMAC', hash: 'SHA-256', length: 256 },
     true,
@@ -102,10 +103,10 @@ export async function hkdfHmacKey(
 
 export async function generateHmacSignature(
   secret: Uint8Array,
-  salt: Uint8Array,
+  info: Uint8Array,
   message: Uint8Array
 ): Promise<Uint8Array> {
-  const key = await hkdfHmacKey(secret, salt)
+  const key = await hkdfHmacKey(secret, info)
   const signed = await crypto.subtle.sign('HMAC', key, message)
   return new Uint8Array(signed)
 }

diff --git a/src/keystore/InMemoryKeystore.ts b/src/keystore/InMemoryKeystore.ts
@@ -305,10 +305,10 @@ export default class InMemoryKeystore implements KeystoreInterface {
         const thirtyDayPeriodsSinceEpoch = Math.floor(
           Date.now() / 1000 / 60 / 60 / 24 / 30
         )
-        const salt = `${thirtyDayPeriodsSinceEpoch}-${this.accountAddress}`
+        const info = `${thirtyDayPeriodsSinceEpoch}-${this.accountAddress}`
         const hmac = await generateHmacSignature(
           keyMaterial,
-          new TextEncoder().encode(salt),
+          new TextEncoder().encode(info),
           headerBytes
         )
 

diff --git a/test/crypto/encryption.test.ts b/test/crypto/encryption.test.ts
@@ -10,32 +10,42 @@ import crypto from '../../src/crypto/crypto'
 describe('HMAC encryption', () => {
   it('generates and validates HMAC', async () => {
     const secret = crypto.getRandomValues(new Uint8Array(32))
-    const salt = crypto.getRandomValues(new Uint8Array(32))
+    const info = crypto.getRandomValues(new Uint8Array(32))
     const message = crypto.getRandomValues(new Uint8Array(32))
-    const hmac = await generateHmacSignature(secret, salt, message)
-    const key = await hkdfHmacKey(secret, salt)
+    const hmac = await generateHmacSignature(secret, info, message)
+    const key = await hkdfHmacKey(secret, info)
     const valid = await verifyHmacSignature(key, hmac, message)
     expect(valid).toBe(true)
   })
 
   it('generates and validates HMAC with imported key', async () => {
     const secret = crypto.getRandomValues(new Uint8Array(32))
-    const salt = crypto.getRandomValues(new Uint8Array(32))
+    const info = crypto.getRandomValues(new Uint8Array(32))
     const message = crypto.getRandomValues(new Uint8Array(32))
-    const hmac = await generateHmacSignature(secret, salt, message)
-    const key = await hkdfHmacKey(secret, salt)
+    const hmac = await generateHmacSignature(secret, info, message)
+    const key = await hkdfHmacKey(secret, info)
     const exportedKey = await exportHmacKey(key)
     const importedKey = await importHmacKey(exportedKey)
     const valid = await verifyHmacSignature(importedKey, hmac, message)
     expect(valid).toBe(true)
   })
 
+  it('generates different HMAC keys with different infos', async () => {
+    const secret = crypto.getRandomValues(new Uint8Array(32))
+    const info1 = crypto.getRandomValues(new Uint8Array(32))
+    const info2 = crypto.getRandomValues(new Uint8Array(32))
+    const key1 = await hkdfHmacKey(secret, info1)
+    const key2 = await hkdfHmacKey(secret, info2)
+
+    expect(await exportHmacKey(key1)).not.toEqual(await exportHmacKey(key2))
+  })
+
   it('fails to validate HMAC with wrong message', async () => {
     const secret = crypto.getRandomValues(new Uint8Array(32))
-    const salt = crypto.getRandomValues(new Uint8Array(32))
+    const info = crypto.getRandomValues(new Uint8Array(32))
     const message = crypto.getRandomValues(new Uint8Array(32))
-    const hmac = await generateHmacSignature(secret, salt, message)
-    const key = await hkdfHmacKey(secret, salt)
+    const hmac = await generateHmacSignature(secret, info, message)
+    const key = await hkdfHmacKey(secret, info)
     const valid = await verifyHmacSignature(
       key,
       hmac,
@@ -46,9 +56,9 @@ describe('HMAC encryption', () => {
 
   it('fails to validate HMAC with wrong key', async () => {
     const secret = crypto.getRandomValues(new Uint8Array(32))
-    const salt = crypto.getRandomValues(new Uint8Array(32))
+    const info = crypto.getRandomValues(new Uint8Array(32))
     const message = crypto.getRandomValues(new Uint8Array(32))
-    const hmac = await generateHmacSignature(secret, salt, message)
+    const hmac = await generateHmacSignature(secret, info, message)
     const valid = await verifyHmacSignature(
       await hkdfHmacKey(
         crypto.getRandomValues(new Uint8Array(32)),