diff --git a/sys/crypto/aes.c b/sys/crypto/aes.c
index 0e7fd6a75d..a6a229df83 100644
--- a/sys/crypto/aes.c
+++ b/sys/crypto/aes.c
@@ -45,7 +45,6 @@
  */
 static const cipher_interface_t aes_interface = {
     AES_BLOCK_SIZE,
-    AES_KEY_SIZE,
     aes_init,
     aes_encrypt,
     aes_decrypt
diff --git a/sys/crypto/ciphers.c b/sys/crypto/ciphers.c
index e51fa72fad..1b8afa60de 100644
--- a/sys/crypto/ciphers.c
+++ b/sys/crypto/ciphers.c
@@ -22,13 +22,8 @@
 int cipher_init(cipher_t *cipher, cipher_id_t cipher_id, const uint8_t *key,
                 uint8_t key_size)
 {
-    if (key_size > cipher_id->max_key_size) {
-        return CIPHER_ERR_INVALID_KEY_SIZE;
-    }
-
     cipher->interface = cipher_id;
     return cipher->interface->init(&cipher->context, key, key_size);
-
 }
 
 
diff --git a/sys/include/crypto/ciphers.h b/sys/include/crypto/ciphers.h
index 5c7b24b8e8..d66e7a54e4 100644
--- a/sys/include/crypto/ciphers.h
+++ b/sys/include/crypto/ciphers.h
@@ -73,20 +73,22 @@ typedef struct {
  * @brief   BlockCipher-Interface for the Cipher-Algorithms
  */
 typedef struct cipher_interface_st {
-    /** Blocksize of this cipher */
+    /** @brief Blocksize of this cipher */
     uint8_t block_size;
 
-    /** Maximum key size for this cipher */
-    uint8_t max_key_size;
-
-    /** the init function */
+    /**
+     * @brief the init function.
+     *
+     * This function is responsible for checking that the given key_size is
+     * valid for the chosen cipher.
+     */
     int (*init)(cipher_context_t *ctx, const uint8_t *key, uint8_t key_size);
 
-    /** the encrypt function */
+    /** @brief the encrypt function */
     int (*encrypt)(const cipher_context_t *ctx, const uint8_t *plain_block,
                    uint8_t *cipher_block);
 
-    /** the decrypt function */
+    /** @brief the decrypt function */
     int (*decrypt)(const cipher_context_t *ctx, const uint8_t *cipher_block,
                    uint8_t *plain_block);
 } cipher_interface_t;