diff --git a/lib/error.c b/lib/error.c
index a4dd16f..6505ab6 100644
--- a/lib/error.c
+++ b/lib/error.c
@@ -46,6 +46,8 @@ static const err_t errors[] = {
   ERR (YKPIV_PCSC_ERROR, "Error in PCSC call"),
   ERR (YKPIV_SIZE_ERROR, "Wrong buffer size"),
   ERR (YKPIV_APPLET_ERROR, "No PIV applet found"),
+  ERR (YKPIV_AUTHENTICATION_ERROR, "Error during authentication"),
+  ERR (YKPIV_RANDOMNESS_ERROR, "Error getting randomness"),
 };
 
 /**
diff --git a/lib/ykpiv.c b/lib/ykpiv.c
index 0db5dca..de2a434 100644
--- a/lib/ykpiv.c
+++ b/lib/ykpiv.c
@@ -32,6 +32,9 @@
 #include <stdio.h>
 #include <stdint.h>
 
+#include <openssl/des.h>
+#include <openssl/rand.h>
+
 #include "internal.h"
 #include "ykpiv.h"
 
@@ -270,3 +273,89 @@ ykpiv_rc ykpiv_send_data(ykpiv_state *state, unsigned char *apdu,
   }
   return YKPIV_OK;
 }
+
+ykpiv_rc ykpiv_authenticate(ykpiv_state *state, unsigned const char *key) {
+  APDU apdu;
+  unsigned char data[0xff];
+  DES_cblock challenge;
+  unsigned long recv_len = sizeof(data);
+  int sw;
+  ykpiv_rc res;
+
+  DES_key_schedule ks1, ks2, ks3;
+
+  /* set up our key */
+  {
+    const_DES_cblock key_tmp;
+    memcpy(key_tmp, key, 8);
+    DES_set_key_unchecked(&key_tmp, &ks1);
+    memcpy(key_tmp, key + 8, 8);
+    DES_set_key_unchecked(&key_tmp, &ks2);
+    memcpy(key_tmp, key + 16, 8);
+    DES_set_key_unchecked(&key_tmp, &ks3);
+  }
+
+  /* get a challenge from the card */
+  {
+    memset(apdu.raw, 0, sizeof(apdu));
+    apdu.st.ins = 0x87;
+    apdu.st.p1 = 0x03; /* triple des */
+    apdu.st.p2 = 0x9b; /* management key */
+    apdu.st.lc = 0x04;
+    apdu.st.data[0] = 0x7c;
+    apdu.st.data[1] = 0x02;
+    apdu.st.data[2] = 0x80;
+    if((res = ykpiv_send_data(state, apdu.raw, data, &recv_len, &sw)) != YKPIV_OK) {
+      return res;
+    } else if(sw != 0x9000) {
+      return YKPIV_AUTHENTICATION_ERROR;
+    }
+    memcpy(challenge, data + 4, 8);
+  }
+
+  /* send a response to the cards challenge and a challenge of our own. */
+  {
+    unsigned char *dataptr = apdu.st.data;
+    DES_cblock response;
+    DES_ecb3_encrypt(&challenge, &response, &ks1, &ks2, &ks3, 0);
+
+    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 */
+    *dataptr++ = 0x7c;
+    *dataptr++ = 20; /* 2 + 8 + 2 +8 */
+    *dataptr++ = 0x80;
+    *dataptr++ = 8;
+    memcpy(dataptr, response, 8);
+    dataptr += 8;
+    *dataptr++ = 0x81;
+    *dataptr++ = 8;
+    if(RAND_pseudo_bytes(dataptr, 8) == -1) {
+      if(state->verbose) {
+	fprintf(stderr, "Failed getting randomness for authentication.\n");
+      }
+      return YKPIV_RANDOMNESS_ERROR;
+    }
+    memcpy(challenge, dataptr, 8);
+    dataptr += 8;
+    apdu.st.lc = dataptr - apdu.st.data;
+    if((res = ykpiv_send_data(state, apdu.raw, data, &recv_len, &sw)) != YKPIV_OK) {
+      return res;
+    } else if(sw != 0x9000) {
+      return YKPIV_AUTHENTICATION_ERROR;
+    }
+  }
+
+  /* compare the response from the card with our challenge */
+  {
+    DES_cblock response;
+    DES_ecb3_encrypt(&challenge, &response, &ks1, &ks2, &ks3, 1);
+    if(memcmp(response, data + 4, 8) == 0) {
+      return YKPIV_OK;
+    } else {
+      return YKPIV_AUTHENTICATION_ERROR;
+    }
+  }
+}
diff --git a/lib/ykpiv.h b/lib/ykpiv.h
index 5e65243..7253198 100644
--- a/lib/ykpiv.h
+++ b/lib/ykpiv.h
@@ -45,6 +45,8 @@ extern "C"
 		YKPIV_PCSC_ERROR = -2,
 		YKPIV_SIZE_ERROR = -3,
 		YKPIV_APPLET_ERROR = -4,
+		YKPIV_AUTHENTICATION_ERROR = -5,
+		YKPIV_RANDOMNESS_ERROR = -6,
 	} ykpiv_rc;
 
 	const char *ykpiv_strerror(ykpiv_rc err);
@@ -58,6 +60,7 @@ extern "C"
 			unsigned char *out_data, unsigned long *out_len, int *sw);
 	ykpiv_rc ykpiv_send_data(ykpiv_state *state, unsigned char *apdu,
 			unsigned char *data, unsigned long *recv_len, int *sw);
+	ykpiv_rc ykpiv_authenticate(ykpiv_state *state, const unsigned char *key);
 
 #ifdef __cplusplus
 }
diff --git a/lib/ykpiv.map b/lib/ykpiv.map
index 1554d62..a6812ce 100644
--- a/lib/ykpiv.map
+++ b/lib/ykpiv.map
@@ -35,6 +35,7 @@ global:
 	ykpiv_connect;
 	ykpiv_send_data;
 	ykpiv_transfer_data;
+	ykpiv_authenticate;
 
 local:
 	*;
diff --git a/tool/yubico-piv-tool.c b/tool/yubico-piv-tool.c
index 6c73355..3bbcd37 100644
--- a/tool/yubico-piv-tool.c
+++ b/tool/yubico-piv-tool.c
@@ -90,89 +90,6 @@ static bool sign_data(ykpiv_state*, unsigned char*, int, unsigned char, unsigned
     ASN1_BIT_STRING*);
 static int get_object_id(enum enum_slot slot);
 
-static bool authenticate(ykpiv_state *state, unsigned const char *key) {
-  APDU apdu;
-  unsigned char data[0xff];
-  DES_cblock challenge;
-  unsigned long recv_len = sizeof(data);
-  int sw;
-
-  DES_key_schedule ks1, ks2, ks3;
-
-  /* set up our key */
-  {
-    const_DES_cblock key_tmp;
-    memcpy(key_tmp, key, 8);
-    DES_set_key_unchecked(&key_tmp, &ks1);
-    memcpy(key_tmp, key + 8, 8);
-    DES_set_key_unchecked(&key_tmp, &ks2);
-    memcpy(key_tmp, key + 16, 8);
-    DES_set_key_unchecked(&key_tmp, &ks3);
-  }
-
-  /* get a challenge from the card */
-  {
-    memset(apdu.raw, 0, sizeof(apdu));
-    apdu.st.ins = 0x87;
-    apdu.st.p1 = 0x03; /* triple des */
-    apdu.st.p2 = 0x9b; /* management key */
-    apdu.st.lc = 0x04;
-    apdu.st.data[0] = 0x7c;
-    apdu.st.data[1] = 0x02;
-    apdu.st.data[2] = 0x80;
-    if(ykpiv_send_data(state, apdu.raw, data, &recv_len, &sw) != YKPIV_OK) {
-      return false;
-    } else if(sw != 0x9000) {
-      return false;
-    }
-    memcpy(challenge, data + 4, 8);
-  }
-
-  /* send a response to the cards challenge and a challenge of our own. */
-  {
-    unsigned char *dataptr = apdu.st.data;
-    DES_cblock response;
-    DES_ecb3_encrypt(&challenge, &response, &ks1, &ks2, &ks3, 0);
-
-    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 */
-    *dataptr++ = 0x7c;
-    *dataptr++ = 20; /* 2 + 8 + 2 +8 */
-    *dataptr++ = 0x80;
-    *dataptr++ = 8;
-    memcpy(dataptr, response, 8);
-    dataptr += 8;
-    *dataptr++ = 0x81;
-    *dataptr++ = 8;
-    if(RAND_pseudo_bytes(dataptr, 8) == -1) {
-      fprintf(stderr, "Failed getting randomness for authentication.\n");
-      return false;
-    }
-    memcpy(challenge, dataptr, 8);
-    dataptr += 8;
-    apdu.st.lc = dataptr - apdu.st.data;
-    if(ykpiv_send_data(state, apdu.raw, data, &recv_len, &sw) != YKPIV_OK) {
-      return false;
-    } else if(sw != 0x9000) {
-      return false;
-    }
-  }
-
-  /* compare the response from the card with our challenge */
-  {
-    DES_cblock response;
-    DES_ecb3_encrypt(&challenge, &response, &ks1, &ks2, &ks3, 1);
-    if(memcmp(response, data + 4, 8) == 0) {
-      return true;
-    } else {
-      return false;
-    }
-  }
-}
-
 static void print_version(ykpiv_state *state) {
   APDU apdu;
   unsigned char data[0xff];
@@ -1288,7 +1205,7 @@ int main(int argc, char *argv[]) {
     return EXIT_FAILURE;
   }
 
-  if(authenticate(state, key) == false) {
+  if(ykpiv_authenticate(state, key) != YKPIV_OK) {
     fprintf(stderr, "Failed authentication with the applet.\n");
     return EXIT_FAILURE;
   }