diff --git a/src/misc.ts b/src/misc.ts
index b9e41d2..5992c40 100644
--- a/src/misc.ts
+++ b/src/misc.ts
@@ -11,13 +11,31 @@ export enum Usage {
 
 export async function pubkey_toString(pubkey: CryptoKey): Promise<string> {
   log.trace('pubkey_toString')
+
   const pubkey_buff = await crypto.subtle.exportKey('spki', pubkey)
-  return a2b64(new Uint8Array(pubkey_buff))
+  const pubkey_str = a2b64(new Uint8Array(pubkey_buff))
+
+  const usage = (pubkey.usages.includes('verify') ? Usage.sign : Usage.ecdh).toString()
+
+  return `${usage}${pubkey_str}`
 }
-export async function pubkey_fromString(pubkey_str: string, usage: Usage): Promise<CryptoKey | null> {
+export async function pubkey_fromString(pubkey_str: string): Promise<CryptoKey | null> {
   log.trace('pubkey_fromString')
 
-  const pubkey = b642a(pubkey_str)
+  let usage: Usage;
+  const c = pubkey_str.at(0)
+  if (c === undefined) {
+    log.warn('Empty string ?')
+    return null
+  } else if (c === Usage.sign.toString()) usage = Usage.sign
+  else if (c === Usage.ecdh.toString()) usage = Usage.ecdh
+  else {
+    log.warn('Unknown usage encoded')
+    log.debug('Usage :', c)
+    return null
+  }
+
+  const pubkey = b642a(pubkey_str.slice(1))
   if (pubkey === null) return null
 
   try {
@@ -37,15 +55,32 @@ export async function pubkey_fromString(pubkey_str: string, usage: Usage): Promi
 
 export async function pubkey_toBytes(pubkey: CryptoKey): Promise<Uint8Array> {
   log.trace('pubkey_toBytes')
-  return new Uint8Array(await crypto.subtle.exportKey('raw', pubkey))
+
+  const buf = new Uint8Array(await crypto.subtle.exportKey('raw', pubkey))
+  const usage = pubkey.usages.includes('verify') ? Usage.sign : Usage.ecdh
+
+  return new Uint8Array([usage, ...buf])
 }
-export async function pubkey_fromBytes(pubkey: Uint8Array, usage: Usage): Promise<CryptoKey | null> {
+export async function pubkey_fromBytes(pubkey: Uint8Array): Promise<CryptoKey | null> {
   log.trace('pubkey_fromBytes')
 
+  let usage: Usage;
+  const o = pubkey.at(0)
+  if (o === undefined) {
+    log.warn('Empty array ?')
+    return null
+  } else if (o === Usage.sign) usage = Usage.sign
+  else if (o === Usage.ecdh) usage = Usage.ecdh
+  else {
+    log.warn('Unknown usage encoded')
+    log.debug('Usage :', o)
+    return null
+  }
+
   try {
     return await crypto.subtle.importKey(
       'raw',
-      pubkey,
+      pubkey.slice(1),
       usage === Usage.ecdh ? ECDH_PARAMETERS() : SIGNATURE_KEY(),
       true,
       usage === Usage.ecdh ? [] : ['verify']
diff --git a/src/private-box.ts b/src/private-box.ts
index 03e0915..5bc8e31 100644
--- a/src/private-box.ts
+++ b/src/private-box.ts
@@ -75,7 +75,7 @@ export default class PrivateBox {
       log.warn('Data too short to contain pubkey')
       return null
     }
-    const pubkey = await pubkey_fromBytes(pubkey_buff, Usage.ecdh)
+    const pubkey = await pubkey_fromBytes(pubkey_buff)
     if (pubkey === null) return null
 
     const box = SecretBox.fromBytes(data.slice(1 + length))
@@ -88,6 +88,6 @@ export default class PrivateBox {
     return await misc.pubkey_toString(pubkey)
   }
   public static async pubkey_fromString(pubkey: string): Promise<CryptoKey | null> {
-    return await misc.pubkey_fromString(pubkey, misc.Usage.ecdh)
+    return await misc.pubkey_fromString(pubkey)
   }
 }
diff --git a/src/private-wrap.ts b/src/private-wrap.ts
index a665204..8f347cd 100644
--- a/src/private-wrap.ts
+++ b/src/private-wrap.ts
@@ -63,6 +63,6 @@ export default class PrivateWrap {
     return await misc.pubkey_toString(pubkey)
   }
   public static async pubkey_fromString(pubkey: string): Promise<CryptoKey | null> {
-    return await misc.pubkey_fromString(pubkey, misc.Usage.ecdh)
+    return await misc.pubkey_fromString(pubkey)
   }
 }
diff --git a/src/signature.ts b/src/signature.ts
index 73e6562..8be0d66 100644
--- a/src/signature.ts
+++ b/src/signature.ts
@@ -37,7 +37,7 @@ export async function pubkey_toString(pubkey: CryptoKey): Promise<string> {
   return await misc.pubkey_toString(pubkey)
 }
 export async function pubkey_fromString(pubkey: string): Promise<CryptoKey | null> {
-  return await misc.pubkey_fromString(pubkey, misc.Usage.sign)
+  return await misc.pubkey_fromString(pubkey)
 }
 
 export function signature_toString(signature: Uint8Array): string {
diff --git a/test/misc.test.ts b/test/misc.test.ts
index d165d09..a8c6c45 100644
--- a/test/misc.test.ts
+++ b/test/misc.test.ts
@@ -1,13 +1,13 @@
 import {expect, test} from 'bun:test'
 import {PrivateBox, PrivateWrap, SecretBox, signature} from '..'
-import {pubkey_fromBytes, pubkey_fromString, pubkey_toBytes, pubkey_toString, Usage} from '../src/misc'
+import {pubkey_fromBytes, pubkey_fromString, pubkey_toBytes, pubkey_toString} from '../src/misc'
 
 test('Private box', async () => {
   const message = crypto.getRandomValues(new Uint8Array(8))
   const k = await PrivateBox.gen(false)
 
   const ser = await pubkey_toString(k.publicKey)
-  const de = await pubkey_fromString(ser, Usage.ecdh)
+  const de = await pubkey_fromString(ser)
   expect(de).not.toBeNull()
 
   const box = await PrivateBox.encrypt(message, de!)
@@ -19,7 +19,7 @@ test('Private wrap', async () => {
   const k = await PrivateWrap.gen(false)
 
   const ser = await pubkey_toString(k.publicKey)
-  const de = await pubkey_fromString(ser, Usage.ecdh)
+  const de = await pubkey_fromString(ser)
   expect(de).not.toBeNull()
 
   const message = crypto.getRandomValues(new Uint8Array(8))
@@ -42,7 +42,7 @@ test('Signature', async () => {
   expect(signed).not.toBeNull()
 
   const ser = await pubkey_toString(k.publicKey)
-  const de = await pubkey_fromString(ser, Usage.sign)
+  const de = await pubkey_fromString(ser)
   expect(de).not.toBeNull()
 
   const verification = await signature.verify(message, de!, signed!)
@@ -55,7 +55,7 @@ test('Byte serialization', async () => {
   expect(signed).not.toBeNull()
 
   const ser = await pubkey_toBytes(k.publicKey)
-  const de = await pubkey_fromBytes(ser, Usage.sign)
+  const de = await pubkey_fromBytes(ser)
   expect(de).not.toBeNull()
 
   const verification = await signature.verify(message, de!, signed!)