diff --git a/lib/ykpiv.c b/lib/ykpiv.c
index d588e19..7aa8b3b 100644
--- a/lib/ykpiv.c
+++ b/lib/ykpiv.c
@@ -307,9 +307,9 @@ ykpiv_rc ykpiv_authenticate(ykpiv_state *state, unsigned const char *key) {
 
     recv_len = 0xff;
     memset(apdu.raw, 0, sizeof(apdu));
-    apdu.st.ins = 0x87;
-    apdu.st.p1 = 0x03; /* triple des */
-    apdu.st.p2 = 0x9b; /* management key */
+    apdu.st.ins = YKPIV_INS_AUTHENTICATE;
+    apdu.st.p1 = YKPIV_ALGO_3DES; /* triple des */
+    apdu.st.p2 = YKPIV_KEY_CARDMGM; /* management key */
     *dataptr++ = 0x7c;
     *dataptr++ = 20; /* 2 + 8 + 2 +8 */
     *dataptr++ = 0x80;
diff --git a/lib/ykpiv.h b/lib/ykpiv.h
index 662cb6d..01d1136 100644
--- a/lib/ykpiv.h
+++ b/lib/ykpiv.h
@@ -62,6 +62,19 @@ extern "C"
 			unsigned char *data, unsigned long *recv_len, int *sw);
 	ykpiv_rc ykpiv_authenticate(ykpiv_state *state, const unsigned char *key);
 
+#define YKPIV_ALGO_3DES 0x03;
+#define YKPIV_ALGO_RSA1024 0x06;
+#define YKPIV_ALGO_RSA2048 0x07;
+#define YKPIV_ALGO_ECCP256 0x11;
+
+#define YKPIV_KEY_AUTHENTICATION 0x9a;
+#define YKPIV_KEY_CARDMGM 0x9b;
+#define YKPIV_KEY_SIGNATURE 0x9c;
+#define YKPIV_KEY_KEYMGM 0x9d;
+#define YKPIV_KEY_CARDAUTH 0x9e;
+
+#define YKPIV_INS_AUTHENTICATE 0x87;
+
 #ifdef __cplusplus
 }
 #endif