diff --git a/src/modules/_Crypto/hash_submodule.doc b/src/modules/_Crypto/hash_submodule.doc
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+A hash sub-module needs to implement the following Pike-functions:
+
+void update(string);		/* Add this string to the hash */
+string digest(void);		/* Get the digest, and reset the state */
+int query_digest_size(void);	/* Returns the size of the digest */
+string name(void);		/* Name of the algorithm */