PrivateKey (Javadocs [I2P+ 2.13.0+]

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
Default key size in bytes (256 for ElGamal).
- Fields inherited from class net.i2p.data.SimpleDataStructure
  _data

Fields
Modifier and Type	Field and Description
`static int`	`KEYSIZE_BYTES` Default key size in bytes (256 for ElGamal).

Constructor Summary

Constructors
Constructor and Description
`PrivateKey()` no-arg constructor, uses default type
`PrivateKey(byte[] data)` Construct from raw key data.
`PrivateKey(EncType type)` Constructor with type.
`PrivateKey(EncType type, byte[] data)` Constructor with type and data.
`PrivateKey(EncType type, byte[] data, PublicKey pubKey)` Constructor with type, data, and cached public key.
`PrivateKey(String base64Data)` Constructs from base64.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`destroy()` javax.security.auth.Destroyable interface
`boolean`	`equals(Object obj)` Compares this private key with another object for equality.
`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()` Key length in bytes, determined by the encryption type.
`PublicKey`	`toPublic()` Derives a new PublicKey object derived from the secret contents of this PrivateKey.
`String`	`toString()` Returns a string representation of this data structure.

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
```
    Default key size in bytes (256 for ElGamal).
- Constructor Detail
  - PrivateKey
```
public PrivateKey()
```
    no-arg constructor, uses default type
  - PrivateKey
```
public PrivateKey(byte[] data)
```
    Construct from raw key data.
    Parameters:
    data - key data
  - PrivateKey
```
public PrivateKey(EncType type)
```
    Constructor with type.
    Parameters:
    type - non-null
  - PrivateKey
```
public PrivateKey(EncType type,
                  byte[] data)
```
    Constructor with type and data.
    Parameters:
    type - non-null
    data - must be non-null
  - PrivateKey
```
public PrivateKey(EncType type,
                  byte[] data,
                  PublicKey pubKey)
```
    Constructor with type, data, and cached public key.
    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 - if the data is not valid
- Method Detail
  - destroy
```
public void destroy()
```
    javax.security.auth.Destroyable interface
    Specified by:
    destroy in interface Destroyable
  - equals
```
public boolean equals(Object obj)
```
    Compares this private key with another object for equality.
    Overrides:
    equals in class SimpleDataStructure
    Parameters:
    obj - the object to compare
    Returns:
    true if equal
  - 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
    Returns:
    the hash code
  - isDestroyed
```
public boolean isDestroyed()
```
    javax.security.auth.Destroyable interface
    Specified by:
    isDestroyed in interface Destroyable
    Returns:
    whether destroyed
  - length
```
public int length()
```
    Key length in bytes, determined by the encryption type.
    Specified by:
    length in class SimpleDataStructure
    Returns:
    the legal length of the byte array
  - 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()
```
    Description copied from class: SimpleDataStructure
    Returns a string representation of this data structure.
    Overrides:
    toString in class SimpleDataStructure

Class PrivateKey

Field Summary

Fields inherited from class net.i2p.data.SimpleDataStructure

Constructor Summary

Method Summary

Methods inherited from class net.i2p.data.SimpleDataStructure

Methods inherited from class java.lang.Object

Field Detail

KEYSIZE_BYTES

Constructor Detail

PrivateKey

PrivateKey

PrivateKey

PrivateKey

PrivateKey

PrivateKey

Method Detail

destroy

equals

getType

hashCode

isDestroyed

length

toPublic

toString