diff --git a/libfreefare/freefare.h b/libfreefare/freefare.h
index b03ece2..b751d5f 100644
--- a/libfreefare/freefare.h
+++ b/libfreefare/freefare.h
@@ -389,14 +389,14 @@ int		 mifare_desfire_clear_record_file (MifareTag tag, uint8_t file_no);
 int		 mifare_desfire_commit_transaction (MifareTag tag);
 int		 mifare_desfire_abort_transaction (MifareTag tag);
 
-MifareDESFireKey mifare_desfire_des_key_new (uint8_t value[8]);
-MifareDESFireKey mifare_desfire_3des_key_new (uint8_t value[16]);
-MifareDESFireKey mifare_desfire_des_key_new_with_version (uint8_t value[8]);
-MifareDESFireKey mifare_desfire_3des_key_new_with_version (uint8_t value[16]);
-MifareDESFireKey mifare_desfire_3k3des_key_new (uint8_t value[24]);
-MifareDESFireKey mifare_desfire_3k3des_key_new_with_version (uint8_t value[24]);
-MifareDESFireKey mifare_desfire_aes_key_new (uint8_t value[16]);
-MifareDESFireKey mifare_desfire_aes_key_new_with_version (uint8_t value[16], uint8_t version);
+MifareDESFireKey mifare_desfire_des_key_new (const uint8_t value[8]);
+MifareDESFireKey mifare_desfire_3des_key_new (const uint8_t value[16]);
+MifareDESFireKey mifare_desfire_des_key_new_with_version (const uint8_t value[8]);
+MifareDESFireKey mifare_desfire_3des_key_new_with_version (const uint8_t value[16]);
+MifareDESFireKey mifare_desfire_3k3des_key_new (const uint8_t value[24]);
+MifareDESFireKey mifare_desfire_3k3des_key_new_with_version (const uint8_t value[24]);
+MifareDESFireKey mifare_desfire_aes_key_new (const uint8_t value[16]);
+MifareDESFireKey mifare_desfire_aes_key_new_with_version (const uint8_t value[16], uint8_t version);
 uint8_t		 mifare_desfire_key_get_version (MifareDESFireKey key);
 void		 mifare_desfire_key_set_version (MifareDESFireKey key, uint8_t version);
 void		 mifare_desfire_key_free (MifareDESFireKey key);
diff --git a/libfreefare/freefare_internal.h b/libfreefare/freefare_internal.h
index f4c9023..c95dd2a 100644
--- a/libfreefare/freefare_internal.h
+++ b/libfreefare/freefare_internal.h
@@ -243,7 +243,7 @@ struct mifare_desfire_tag {
     uint32_t selected_application;
 };
 
-MifareDESFireKey mifare_desfire_session_key_new (uint8_t rnda[], uint8_t rndb[], MifareDESFireKey authentication_key);
+MifareDESFireKey mifare_desfire_session_key_new (const uint8_t rnda[], const uint8_t rndb[], MifareDESFireKey authentication_key);
 const char	*mifare_desfire_error_lookup (uint8_t error);
 
 struct mifare_ultralight_tag {
diff --git a/libfreefare/mifare_desfire_key.c b/libfreefare/mifare_desfire_key.c
index ebf18c9..c14068a 100644
--- a/libfreefare/mifare_desfire_key.c
+++ b/libfreefare/mifare_desfire_key.c
@@ -38,7 +38,7 @@ update_key_schedules (MifareDESFireKey key)
 }
 
 MifareDESFireKey
-mifare_desfire_des_key_new (uint8_t value[8])
+mifare_desfire_des_key_new (const uint8_t value[8])
 {
     uint8_t data[8];
     memcpy (data, value, 8);
@@ -48,7 +48,7 @@ mifare_desfire_des_key_new (uint8_t value[8])
 }
 
 MifareDESFireKey
-mifare_desfire_des_key_new_with_version (uint8_t value[8])
+mifare_desfire_des_key_new_with_version (const uint8_t value[8])
 {
     MifareDESFireKey key;
 
@@ -62,7 +62,7 @@ mifare_desfire_des_key_new_with_version (uint8_t value[8])
 }
 
 MifareDESFireKey
-mifare_desfire_3des_key_new (uint8_t value[16])
+mifare_desfire_3des_key_new (const uint8_t value[16])
 {
     uint8_t data[16];
     memcpy (data, value, 16);
@@ -74,7 +74,7 @@ mifare_desfire_3des_key_new (uint8_t value[16])
 }
 
 MifareDESFireKey
-mifare_desfire_3des_key_new_with_version (uint8_t value[16])
+mifare_desfire_3des_key_new_with_version (const uint8_t value[16])
 {
     MifareDESFireKey key;
 
@@ -87,7 +87,7 @@ mifare_desfire_3des_key_new_with_version (uint8_t value[16])
 }
 
 MifareDESFireKey
-mifare_desfire_3k3des_key_new (uint8_t value[24])
+mifare_desfire_3k3des_key_new (const uint8_t value[24])
 {
     uint8_t data[24];
     memcpy (data, value, 24);
@@ -97,7 +97,7 @@ mifare_desfire_3k3des_key_new (uint8_t value[24])
 }
 
 MifareDESFireKey
-mifare_desfire_3k3des_key_new_with_version (uint8_t value[24])
+mifare_desfire_3k3des_key_new_with_version (const uint8_t value[24])
 {
     MifareDESFireKey key;
 
@@ -110,13 +110,13 @@ mifare_desfire_3k3des_key_new_with_version (uint8_t value[24])
 }
 
 MifareDESFireKey
-mifare_desfire_aes_key_new (uint8_t value[16])
+mifare_desfire_aes_key_new (const uint8_t value[16])
 {
     return mifare_desfire_aes_key_new_with_version (value, 0);
 }
 
 MifareDESFireKey
-mifare_desfire_aes_key_new_with_version (uint8_t value[16], uint8_t version)
+mifare_desfire_aes_key_new_with_version (const uint8_t value[16], uint8_t version)
 {
     MifareDESFireKey key;
 
@@ -158,7 +158,7 @@ mifare_desfire_key_set_version (MifareDESFireKey key, uint8_t version)
 }
 
 MifareDESFireKey
-mifare_desfire_session_key_new (uint8_t rnda[], uint8_t rndb[], MifareDESFireKey authentication_key)
+mifare_desfire_session_key_new (const uint8_t rnda[], const uint8_t rndb[], MifareDESFireKey authentication_key)
 {
     MifareDESFireKey key = NULL;