diff --git a/src/modules/_Crypto/crypto_submodule.doc b/src/modules/_Crypto/crypto_submodule.doc
index edaf263a591a202125889837d2bf5d9b2eb6b036..31d59456f5026fbda2ed351c124a92c218a4d281 100644
--- a/src/modules/_Crypto/crypto_submodule.doc
+++ b/src/modules/_Crypto/crypto_submodule.doc
@@ -2,9 +2,18 @@ A block crypto sub-module needs to implement the following Pike-functions to
 support encryption/decryption:
 
 int query_block_size(void);	/* Returns the size of the crypt block */
-int query_key_length(void);	/* Returns the minimum key length */
+int query_key_length(void);	/* Returns the minimum length, or 0 if
+				 * key length is variable */
 object set_encrypt_key(mixed);	/* Sets the encryption key. Returns object */
 object set_decrypt_key(mixed);	/* Sets the decryption key. Returns object */
 string crypt_block(string);	/* Crypt the blocks with the current key */
 string name(void);		/* Name of the algorithm */
 
+A stream crypto sub-module must implement the following functions:
+
+int query_key_length(void);	/* Returns the minimum length, or 0 if
+				 * key length is variable */
+object set_encrypt_key(mixed);  /* Sets encryption key. Returns object */
+object set_decrypt_key(mixed);	/* Sets the decryption key. Returns object */
+string crypt(string);           /* Encrypts string */
+string name(void);              /* Name of algorithm */