 ecdsa_sign(+Key, 
+Data, -Signature, +Options)
ecdsa_sign(+Key, 
+Data, -Signature, +Options)hex) assumes that Data is an atom, 
string, character list or code list representing the data in hexadecimal 
notation. See rsa_sign/4 for an 
example.
Options:
hex. 
Alternatives are octet, utf8 and text.