net.i2p.data

Class PrivateKey

java.lang.Object

net.i2p.data.SimpleDataStructure

net.i2p.data.PrivateKey

All Implemented Interfaces:

Destroyable, DataStructure

public class PrivateKey
extends SimpleDataStructure
implements Destroyable

Cryptographic private key for asymmetric encryption in I2P.

PrivateKey provides the decryption component of I2P's asymmetric cryptography:

• Default Algorithm: ElGamal 2048-bit (256 bytes)
• Modern Support: Variable length and type support since 0.9.38
• Key Structure: Contains only the private exponent
• Security: Implements Destroyable for secure cleanup

Supported Algorithms:

• ElGamal 2048: Legacy algorithm, 256-byte keys
• ECIES X25519: Modern elliptic curve, 32-byte keys
• Future Types: Extensible design for new algorithms

Key Format:

• ElGamal: 256-byte private exponent only
• Constants: Prime numbers defined in crypto specification
• Efficiency: Only stores variable private component
• Validation: Type-specific length and format checking

Usage:

• Decryption: Decrypt messages encrypted with corresponding PublicKey
• Key Exchange: Participate in ElGamal key exchange protocols
• Identity: Part of Destination cryptographic identity
• Storage: Securely stored in keyring or keystore

Security Considerations:

• Confidentiality: Private keys must never be exposed
• Secure Destruction: Call destroy() when no longer needed
• Memory Protection: Zeroize memory after use
• Algorithm Choice: Prefer modern algorithms (X25519) when possible

Performance Features:

• Caching: LRU cache for frequently used keys
• Public Key Derivation: Cached derived public key
• Efficient Storage: Optimized byte representation
• Factory Methods: Static creation methods for cache access

Migration Path:

• Legacy: ElGamal 2048-bit for backward compatibility
• Modern: ECIES X25519 for better performance and security
• Transition: Mixed algorithm support during migration

Thread Safety:

• Immutable Data: Key data cannot be modified after creation
• Safe Destruction: Thread-safe key zeroization
• Cache Access: Thread-safe factory methods

Field Summary

Fields

Modifier and Type	Field and Description
static int	KEYSIZE_BYTES

Fields inherited from class net.i2p.data.SimpleDataStructure

_data

Constructor Summary

Constructors

Constructor and Description
PrivateKey()
PrivateKey(byte[] data)
PrivateKey(EncType type)
PrivateKey(EncType type, byte[] data)
PrivateKey(EncType type, byte[] data, PublicKey pubKey)
PrivateKey(String base64Data) constructs from base64

Method Summary

Modifier and Type	Method and Description
void	destroy() javax.security.auth.Destroyable interface
boolean	equals(Object obj) Warning - this returns true for two different classes with the same size and same data, e.g.
EncType	getType() Gets the encryption type of this private key.
int	hashCode() We assume the data has enough randomness in it, so use the last 4 bytes for speed.
boolean	isDestroyed() javax.security.auth.Destroyable interface
int	length() The legal length of the byte array in this data structure
PublicKey	toPublic() Derives a new PublicKey object derived from the secret contents of this PrivateKey.
String	toString()

Methods inherited from class net.i2p.data.SimpleDataStructure

calculateHash, fromBase64, fromByteArray, getData, read, readBytes, setData, toBase64, toByteArray, writeBytes

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

KEYSIZE_BYTES

public static final int KEYSIZE_BYTES

Constructor Detail

PrivateKey

public PrivateKey()

PrivateKey

public PrivateKey(byte[] data)

PrivateKey

public PrivateKey(EncType type)

Parameters:

type - non-null

PrivateKey

public PrivateKey(EncType type,
                  byte[] data)

Parameters:

type - non-null

data - must be non-null

PrivateKey

public PrivateKey(EncType type,
                  byte[] data,
                  PublicKey pubKey)

Parameters:

type - non-null

data - must be non-null

pubKey - corresponding pubKey to be cached

PrivateKey

public PrivateKey(String base64Data)
           throws DataFormatException

constructs from base64

Parameters:

base64Data - a string of base64 data (the output of .toBase64() called on a prior instance of PrivateKey

Throws:

DataFormatException

Method Detail

destroy

public void destroy()

javax.security.auth.Destroyable interface

Specified by:

destroy in interface Destroyable

equals

public boolean equals(Object obj)

Description copied from class: SimpleDataStructure

Warning - this returns true for two different classes with the same size and same data, e.g. SessionKey and SessionTag, but you wouldn't put them in the same Set, would you?

Overrides:

equals in class SimpleDataStructure

getType

public EncType getType()

Gets the encryption type of this private key.

Returns:

non-null

hashCode

public int hashCode()

We assume the data has enough randomness in it, so use the last 4 bytes for speed. Overridden since we use short exponents, so the first 227 bytes are all zero.

Overrides:

hashCode in class SimpleDataStructure

isDestroyed

public boolean isDestroyed()

javax.security.auth.Destroyable interface

Specified by:

isDestroyed in interface Destroyable

length

public int length()

Description copied from class: SimpleDataStructure

The legal length of the byte array in this data structure

Specified by:

length in class SimpleDataStructure

toPublic

public PublicKey toPublic()

Derives a new PublicKey object derived from the secret contents of this PrivateKey. As of 0.9.44, the PublicKey is cached.

Returns:

a PublicKey object

Throws:

IllegalArgumentException - on bad key

toString

public String toString()

Overrides:

toString in class SimpleDataStructure