-EVP_get_digestbyname() function for example B<sha1>.
-This value is used only for sanity-checking the lengths of data passed in to
-the B<pkeyutl> and for creating the structures that make up the signature
-(e.g. B<DigestInfo> in RSASSA PKCS#1 v1.5 signatures).
-In case of RSA, ECDSA and DSA signatures, this utility
-will not perform hashing on input data but rather use the data directly as
-input of signature algorithm. Depending on key type, signature type and mode
-of padding, the maximum acceptable lengths of input data differ. In general,
-with RSA the signed data can't be longer than the key modulus, in case of ECDSA
-and DSA the data shouldn't be longer than field size, otherwise it will be
-silently truncated to field size.
-
-In other words, if the value of digest is B<sha1> the input should be 20 bytes
-long binary encoding of SHA-1 hash function output.
+EVP_get_digestbyname() function for example B<sha1>. This value is not used to
+hash the input data. It is used (by some algorithms) for sanity-checking the
+lengths of data passed in to the B<pkeyutl> and for creating the structures that
+make up the signature (e.g. B<DigestInfo> in RSASSA PKCS#1 v1.5 signatures).
+
+This utility does not hash the input data but rather it will use the data
+directly as input to the signature algorithm. Depending on the key type,
+signature type, and mode of padding, the maximum acceptable lengths of input
+data differ. The signed data can't be longer than the key modulus with RSA. In
+case of ECDSA and DSA the data shouldn't be longer than the field
+size, otherwise it will be silently truncated to the field size. In any event
+the input size must not be larger than the largest supported digest size.
+
+In other words, if the value of digest is B<sha1> the input should be the 20
+bytes long binary encoding of the SHA-1 hash function output.
+
+The Ed25519 and Ed448 signature algorithms are not supported by this utility.
+They accept non-hashed input, but this utility can only be used to sign hashed
+input.