Destination

net.i2p.data.Destination

All Implemented Interfaces:: Serializable, DataStructure

Direct Known Subclasses:: VerifiedDestination

public class Destinationextends KeysAndCert

Defines an endpoint in the I2P network that can receive messages.

Destination represents the fundamental addressing and identity concept in I2P:

Network Endpoint: Messages sent to a Destination will find it regardless of location
Cryptographic Identity: Contains encryption and signing keys
Certificate: Optional metadata about the identity
Addressing: Can be encoded as Base64 or Base32 (.b32.i2p)
Immutability: Identity becomes immutable after keys are set

Key Components:

Public Encryption Key: Historically used for end-to-end encryption
Signing Public Key: Used for identity verification and LeaseSet signing
Certificate: Optional metadata (NULL, HIDDEN, SIGNED, etc.)
Cached Hash: SHA-256 hash for efficient identification

Address Formats:

Base64: Full binary encoding for configuration files
Base32: Human-readable .b32.i2p addresses
Hash: 32-byte SHA-256 for internal identification

Historical Changes:

Pre-0.6: Public key used for end-to-end encryption
Post-0.6: End-to-end encryption removed, LeaseSet keys used instead
LeaseSet Encryption: Public key first bytes used as IV (deprecated)
0.9.9: Immutable after keys and certificate are set

Usage:

Client Connections: Target for I2P client communications
Service Hosting: Identity for hosting I2P services
Message Routing: Destination for I2NP message delivery
Address Book: Entry in address books and contact lists

Security Considerations:

Key Protection: Private keys must be securely stored
Identity Verification: Always verify signatures from destinations
Certificate Validation: Check certificate types and content
Deprecated Features: Avoid legacy encryption mechanisms

Performance Features:

Caching: LRU cache for frequently used destinations
Lazy Computation: Base32 address computed on demand
Efficient Storage: Optimized memory usage and serialization
Fast Lookup: Hash-based identification for quick comparisons

Immutability:

After 0.9.9: Keys and certificate cannot be changed after setting
Thread Safety: Immutable objects are inherently thread-safe
Corruption Prevention: Protects against accidental modification
Exception: Modification attempts throw IllegalStateException

Migration Notes:

Legacy Encryption: Public key usage deprecated in favor of LeaseSet encryption
Modern Alternatives: Use EncryptedLeaseSet for proper encryption
IV Generation: LeaseSet encryption IV should not use public key bytes

See Also:

Field Summary
Fields
Modifier and Type
Field
Description
private static final Map<SigningPublicKey, Destination>
_cache
Destinations by signing key.
private String
_cachedB64
Cached b64.
private static final int
CACHE_SIZE
Number of destinations cached, sized from free memory.
private static final int
MAX_CACHE_SIZE
Largest destination cache allowed.
private static final int
MIN_CACHE_SIZE
Smallest destination cache allowed.
Fields inherited from class KeysAndCert
_certificate, _paddingBlocks, _publicKey, _signingKey
Modifier and Type
Field
Description
protected Certificate
_certificate
Certificate specifying key types and metadata.
protected int
_paddingBlocks
If compressed, the padding size / 32, else 0.
protected PublicKey
_publicKey
Public encryption key.
protected SigningPublicKey
_signingKey
Public signing key.
Constructor Summary
Modifier
Constructor
Description
Destination()
Empty destination with no data set.
Destination(String s)
Alternative constructor which takes a base64 string representation.
private
Destination(PublicKey pk, SigningPublicKey sk, Certificate c, byte[] padding)
Creates a destination from its components.
Method Summary
Modifier and Type
Method
Description
static void
clearCache()
Clear the cache.
static Destination
create(InputStream in)
Pull from cache or return new.
boolean
equals(Object o)
Compares this Destination for equality with another object.
int
hashCode()
Hash code of this destination.
int
size()
Serialized size of this destination.
String
toBase32()
For convenience.
String
toBase64()
Cache it.
int
writeBytes(byte[] target, int offset)
Deprecated, used only by Packet.java in streaming.
Methods inherited from class KeysAndCert
calculateHash, combinePadding, getCertificate, getEncType, getHash, getPadding, getPublicKey, getSigningPublicKey, getSigType, isCompressible, readBytes, setCertificate, setPadding, setPublicKey, setSigningPublicKey, toString, writeBytes, writePaddingBytes
Modifier and Type
Method
Description
Hash
calculateHash()
Throws IllegalStateException if keys and cert are not initialized, as of 0.9.12.
protected static byte[]
combinePadding(byte[] pad1, byte[] pad2)
Combines two padding arrays.
Certificate
getCertificate()
Certificate for this identity.
EncType
getEncType()
Encryption type from the certificate.
Hash
getHash()
Throws IllegalStateException if keys and cert are not initialized, as of 0.9.12.
byte[]
getPadding()
Padding bytes for key alignment.
PublicKey
getPublicKey()
Valid for RouterIdentities.
SigningPublicKey
getSigningPublicKey()
Signing public key for this identity.
SigType
getSigType()
Signature type from the certificate.
boolean
isCompressible()
Is there compressible padding?
void
readBytes(InputStream in)
Reads the keys and certificate from an input stream.
void
setCertificate(Certificate cert)
Certificate to set.
void
setPadding(byte[] padding)
Padding bytes to set.
void
setPublicKey(PublicKey key)
Public key to set.
void
setSigningPublicKey(SigningPublicKey key)
Signing public key to set.
String
toString()
Returns a string representation of this KeysAndCert.
void
writeBytes(OutputStream out)
Writes the keys and certificate to an output stream.
protected int
writePaddingBytes(byte[] target, int off)
For Destination.writeBytes().
Methods inherited from class DataStructureImpl
fromBase64, fromByteArray, read, toByteArray
Modifier and Type
Method
Description
void
fromBase64(String data)
Load the structure from the provided base64 string.
void
fromByteArray(byte[] data)
Loads structure from the data provided
protected int
read(InputStream in, byte[] target)
Repeated reads until buffer is full or IOException is thrown.
byte[]
toByteArray()
Convert the structure to a byte array.
Methods inherited from class Object
clone, getClass, notify, notifyAll, wait, wait, wait

Field Details
- _cachedB64
  private String _cachedB64
  Cached b64.
- CACHE_SIZE
  private static final int CACHE_SIZE
  Number of destinations cached, sized from free memory.
- MIN_CACHE_SIZE
  private static final int MIN_CACHE_SIZE
  Smallest destination cache allowed.
  See Also:
  Constant Field Values
- MAX_CACHE_SIZE
  private static final int MAX_CACHE_SIZE
  Largest destination cache allowed.
  See Also:
  Constant Field Values
- _cache
  private static final Map<SigningPublicKey, Destination> _cache
  Destinations by signing key.
Constructor Details
- Destination
  public Destination()
  Empty destination with no data set.
- Destination
  public Destination(String s) throws DataFormatException
  Alternative constructor which takes a base64 string representation.
  Parameters:
  s - a Base64 representation of the destination, as (eg) is used in hosts.txt
  Throws:
  DataFormatException - if the string is invalid
- Destination
  private Destination(PublicKey pk, SigningPublicKey sk, Certificate c, byte[] padding)
  Creates a destination from its components.
  Parameters:
  pk - the encryption public key
  sk - the signing public key
  c - the certificate type, usually null
  padding - the lease key padding
Method Details
- create
  public static Destination create(InputStream in) throws DataFormatException, IOException
  Pull from cache or return new.
  Parameters:
  in - the input stream
  Returns:
  the destination read from the stream, shared with any instance already cached under the same signing key
  Throws:
  DataFormatException - if data is invalid
  IOException - if an I/O error occurs
- writeBytes
  public int writeBytes(byte[] target, int offset)
  Deprecated, used only by Packet.java in streaming. Minimal variant of writeBytes(OutputStream) that writes a typed (XDH/PQ) destination too; the KEYSIZE_BYTES hardcode broke 32-byte key destinations with ArrayIndexOutOfBoundsException. Broken for sig types P521 and RSA before 0.9.15.
  Parameters:
  target - the buffer receiving the serialised destination
  offset - the offset to start writing
  Returns:
  the written length (NOT the new offset)
- size
  public int size()
  Serialized size of this destination. Must match writeBytes(byte[], int); the KEYSIZE_BYTES hardcode broke 32-byte key destinations. For typed keys the wire layout is [pk data][pad1][pad2][spk data][cert], so the base is the actual public key length plus the truncated signing key length.
  Returns:
  the size in bytes
- toBase64
  public String toBase64()
  Cache it. Useful in I2PTunnelHTTPServer where it is added to the headers.
  Specified by:
  toBase64 in interface DataStructure
  Overrides:
  toBase64 in class DataStructureImpl
  Returns:
  null on error
- toBase32
  public String toBase32()
  For convenience.
  Returns:
  "{52 chars}.b32.i2p" or null if fields not set.
- clearCache
  public static void clearCache()
  Clear the cache.
- equals
  public boolean equals(Object o)
  Compares this Destination for equality with another object.
  Overrides:
  equals in class KeysAndCert
- hashCode
  public int hashCode()
  Hash code of this destination.
  Overrides:
  hashCode in class KeysAndCert
  Returns:
  the signing key's hash code, or 0 if there is none

Field Summary

Fields inherited from class KeysAndCert

Constructor Summary

Method Summary

Methods inherited from class KeysAndCert

Methods inherited from class DataStructureImpl

Methods inherited from class Object

Field Details

_cachedB64

CACHE_SIZE

MIN_CACHE_SIZE

MAX_CACHE_SIZE

_cache

Constructor Details

Destination

Destination

Method Details

create

writeBytes

size

toBase64

toBase32

clearCache

equals

hashCode