this section gives the syntax for private-key information.
private-key information shall have asn.1 type privatekeyinfo:
privatekeyinfo ::= sequence {
version version,
privatekeyalgorithm privatekeyalgorithmidentifier,
privatekey privatekey,
attributes [0] implicit attributes optional }
version ::= integer
privatekeyalgorithmidentifier ::= algorithmidentifier
privatekey ::= octet string
attributes ::= set of attribute


