class CompositeKey : PublicKey
A tree data structure that enables the representation of composite public keys, which are used to represent the signing requirements for multisignature scenarios such as RAFT notary services. A composite key is a list of leaf keys and their contributing weight, and each leaf can be a conventional single key or a composite key. Keys contribute their weight to the total if they are matched by the signature.
For complex scenarios, such as "Both Alice and Bob need to sign to consume a state S", we can represent the requirement by creating a tree with a root CompositeKey, and Alice and Bob as children. The root node would specify weights for each of its children and a threshold – the minimum total weight required (e.g. the minimum number of child signatures required) to satisfy the tree signature requirement.
Using these constructs we can express e.g. 1 of N (OR) or N of N (AND) signature requirements. By nesting we can create multilevel requirements such as "either the CEO or 3 of 5 of his assistants need to sign".
class Builder
A helper class for building a CompositeKey. 

data class NodeAndWeight : Comparable<NodeAndWeight>, ASN1Object
Holds node  weight pairs for a CompositeKey. Ordered first by weight, then by node's hashCode. Each node should be assigned with a positive weight to avoid certain types of weight underflow attacks. 
val children: List<NodeAndWeight>
Τhe order of the children may not be the same to what was provided in the builder. 

val leafKeys: Set<PublicKey>
Set of all leaf keys of that CompositeKey. 

val threshold: Int
specifies the minimum total weight required (in the simple case – the minimum number of child signatures required) to satisfy the subtree rooted at this node. 
fun checkValidity(): Unit
This method will detect graph cycles in the full composite key structure to protect against infinite loops when traversing the graph and key duplicates in the each layer. It also checks if the threshold and weight constraint requirements are met, while it tests for aggregatedweight integer overflow. In practice, this method should be always invoked on the root CompositeKey, as it inherently validates the child nodes (all the way till the leaves). 

fun equals(other: Any?): Boolean 

fun getAlgorithm(): String 

fun getEncoded(): ByteArray 

fun getFormat(): String 

fun hashCode(): Int 

fun isFulfilledBy(key: PublicKey): Boolean
Takes single PublicKey and checks if CompositeKey requirements hold for that key. fun isFulfilledBy(keysToCheck: Iterable<PublicKey>): Boolean
Function checks if the public keys corresponding to the signatures are matched against the leaves of the composite key tree in question, and the total combined weight of all children is calculated for every intermediary node. If all thresholds are satisfied, the composite key requirement is considered to be met. 

fun toString(): String 
const val KEY_ALGORITHM: String 
fun getInstance(encoded: ByteArray): PublicKey
Build a composite key from a DER encoded form. fun getInstance(asn1: ASN1Primitive): PublicKey 
val PublicKey.keys: Set<PublicKey>
Return a Set of the contained keys if this is a CompositeKey; otherwise, return a Set with a single element (this PublicKey). 
fun PublicKey.containsAny(otherKeys: Iterable<PublicKey>): Boolean
Checks whether any of the given keys matches a leaf on the CompositeKey tree or a single PublicKey. 

fun Any.contextLogger(): Logger
When called from a companion object, returns the logger for the enclosing class. 

fun PublicKey.isFulfilledBy(otherKey: PublicKey): Boolean
Return true if otherKey fulfils the requirements of this PublicKey. fun PublicKey.isFulfilledBy(otherKeys: Iterable<PublicKey>): Boolean
Return true if otherKeys fulfil the requirements of this PublicKey. 

fun PublicKey.isValid(content: ByteArray, signature: DigitalSignature): Boolean
Utility to simplify the act of verifying a signature. In comparison to verify if the key and signature do not match it returns false rather than throwing an exception. Normally you should use the function which throws, as it avoids the risk of failing to test the result, but this is for uses such as java.security.Signature.verify implementations. 

fun PublicKey.toBase58String(): String
Return the Base58 representation of the serialised public key. 

fun PublicKey.toSHA256Bytes(): ByteArray
Return the bytes of the SHA256 output for this public key. 

fun PublicKey.toStringShort(): String
Render a public key to its hash (in Base58) of its serialised form using the DL prefix. 

fun PublicKey.verify(content: ByteArray, signature: DigitalSignature): Boolean
Utility to simplify the act of verifying a signature. fun PublicKey.verify(signatureData: ByteArray, clearData: ByteArray): Boolean
Helper function to verify a signature. 