PBKDF2 params is missing KeyLength (optional field)

[space88man]

The ASN.1 definition of PBKDF2 params omits the optional KeyLength field; if the encoding actually contains the (redundant) KeyLength (redundant because the derived length can be determined from the symmetric algorithm) the Unmarshal step will be wrong.

Current definition:

// kdf_pbkdf2.go
type pbkdf2Params struct {
	Salt           []byte
	IterationCount int
	PRF            pkix.AlgorithmIdentifier `asn1:"optional"`
}

Should be:

type pbkdf2Params struct {
	Salt           []byte
	IterationCount int
        KeyLength  int `asn1:"optional"`
	PRF            pkix.AlgorithmIdentifier `asn1:"optional"`
}

See the correct definition as used by go-pkcs12:
https://github.com/SSLMate/go-pkcs12/blob/fa70679f0f1622a2705336a97225ee8d6c555f96/crypto.go#L200

type pbkdf2Params struct {
        Salt       asn1.RawValue
        Iterations int
        KeyLength  int                      `asn1:"optional"`
        Prf        pkix.AlgorithmIdentifier `asn1:"optional"`
}