diff --git a/src/fido/credential.c b/src/fido/credential.c
index d471378..b68daa3 100644
--- a/src/fido/credential.c
+++ b/src/fido/credential.c
@@ -99,7 +99,7 @@ int credential_create(CborCharString *rpId, CborByteString *userId, CborCharStri
     if (ret != 0) {
         CBOR_ERROR(CTAP1_ERR_OTHER);
     }
-    memcpy(cred_id, "\xf1\xd0\x02\x00", 4);
+    memcpy(cred_id, CRED_PROTO, 4);
     memcpy(cred_id + 4, iv, 12);
 
     err:
@@ -252,7 +252,7 @@ int credential_derive_hmac_key(const uint8_t *cred_id, size_t cred_id_len, uint8
     const mbedtls_md_info_t *md_info = mbedtls_md_info_from_type(MBEDTLS_MD_SHA512);
 
     mbedtls_md_hmac(md_info, outk, 32, (uint8_t *)"SLIP-0022", 9, outk);
-    mbedtls_md_hmac(md_info, outk, 32, (uint8_t *)"\xf1\xd0\x02\x00", 4, outk);
+    mbedtls_md_hmac(md_info, outk, 32, (uint8_t *)CRED_PROTO, 4, outk);
     mbedtls_md_hmac(md_info, outk, 32, (uint8_t *)"hmac-secret", 11, outk);
     mbedtls_md_hmac(md_info, outk, 32, cred_id, cred_id_len, outk);
     return 0;
@@ -266,7 +266,7 @@ int credential_derive_chacha_key(uint8_t *outk) {
     const mbedtls_md_info_t *md_info = mbedtls_md_info_from_type(MBEDTLS_MD_SHA512);
 
     mbedtls_md_hmac(md_info, outk, 32, (uint8_t *)"SLIP-0022", 9, outk);
-    mbedtls_md_hmac(md_info, outk, 32, (uint8_t *)"\xf1\xd0\x02\x00", 4, outk);
+    mbedtls_md_hmac(md_info, outk, 32, (uint8_t *)CRED_PROTO, 4, outk);
     mbedtls_md_hmac(md_info, outk, 32, (uint8_t *)"Encryption key", 14, outk);
     return 0;
 }
diff --git a/src/fido/credential.h b/src/fido/credential.h
index b8ee396..95d5f97 100644
--- a/src/fido/credential.h
+++ b/src/fido/credential.h
@@ -53,6 +53,8 @@ typedef struct Credential
 #define CRED_PROT_UV_OPTIONAL_WITH_LIST     0x02
 #define CRED_PROT_UV_REQUIRED               0x03
 
+#define CRED_PROTO                          "\xf1\xd0\x02\x01"
+
 extern int credential_verify(uint8_t *cred_id, size_t cred_id_len, const uint8_t *rp_id_hash);
 extern int credential_create(CborCharString *rpId, CborByteString *userId, CborCharString *userName, CborCharString *userDisplayName, CredOptions *opts, CredExtensions *extensions, bool use_sign_count, int alg, int curve, uint8_t *cred_id, size_t *cred_id_len);
 extern void credential_free(Credential *cred);