sign
Sign the provided data with the keypair's private key and return a decorated signature.
A decorated signature includes:
The signature hint (last 4 bytes of the public key)
The actual signature bytes
This is the format required for Stellar transaction signatures.
Return
A DecoratedSignature containing the hint and signature
Parameters
data
The data to sign (usually a transaction hash)
Throws
if the private key for this keypair is null