KeyCertificate (Javadocs [I2P+ 2.13.0+]

java.lang.Object
- net.i2p.data.DataStructureImpl
- - net.i2p.data.Certificate
  - - net.i2p.data.KeyCertificate

All Implemented Interfaces:
Serializable, DataStructure
```
public class KeyCertificate
extends Certificate
```
Specialized certificate for defining cryptographic key types used in I2P identities.
KeyCertificate specifies the encryption and signature algorithms for I2P identities:
- Signature Type: Algorithm used for signing (2 bytes)
- Encryption Type: Algorithm used for encryption (2 bytes)
- Excess Data: Additional key-specific data if needed
- Optimized: Frequently used, so has dedicated class for performance
Format Structure:
- Header: 4 bytes total (2-byte sig type + 2-byte crypto type)
- Signature Data: Optional excess data for signature algorithm
- Encryption Data: Optional excess data for encryption algorithm
Supported Combinations:
- ElGamal + DSA-SHA1: Legacy combination (crypto type 0x0000)
- ElGamal + Ed25519: Modern signing with legacy encryption
- ElGamal + ECDSA-P256: Modern signing with legacy encryption
- X25519 + Ed25519: Modern combination (both algorithms)
Predefined Certificates:
- Ed25519: ElGamal + Ed25519 signing key
- ECDSA256: ElGamal + ECDSA-P256 signing key
- X25519_Ed25519: X25519 encryption + Ed25519 signing
Usage:
- Identity Specification: Defines algorithms for Destination
- Algorithm Negotiation: Communicates supported crypto to peers
- Backward Compatibility: Supports legacy and modern algorithms
- Future Proofing: Extensible for new algorithm combinations
Migration Path:
- Legacy: ElGamal encryption (assumed 0x0000) with various signing
- Modern: X25519 encryption with Ed25519 signing
- Transition: Mixed combinations during migration period
Performance Considerations:
- Frequently Used: Every Destination contains a KeyCertificate
- Optimized Creation: Pre-defined certificates for common combinations
- Caching: Immutable instances can be safely shared
See Also:
Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`(package private) static byte[]`	`ECDSA256_PAYLOAD` ElG + P256
`(package private) static byte[]`	`Ed25519_PAYLOAD` ElG + Ed25519
`static KeyCertificate`	`ELG_ECDSA256_CERT` An immutable ElG/ECDSA-P256 certificate.
`static KeyCertificate`	`ELG_Ed25519_CERT` An immutable ElG/Ed25519 certificate.
`static int`	`HEADER_LENGTH` Key certificate header length in bytes.
`static KeyCertificate`	`X25519_Ed25519_CERT` An immutable X25519/Ed25519 certificate.
`(package private) static byte[]`	`X25519_Ed25519_PAYLOAD` X25519 + Ed25519

Fields inherited from class net.i2p.data.Certificate
_payload, _type, CERTIFICATE_LENGTH_SIGNED_WITH_HASH, CERTIFICATE_TYPE_HIDDEN, CERTIFICATE_TYPE_KEY, CERTIFICATE_TYPE_MULTIPLE, CERTIFICATE_TYPE_NULL, CERTIFICATE_TYPE_SIGNED, NULL_CERT

Constructor Summary

Constructors
Constructor and Description
`KeyCertificate(byte[] payload)` 4 bytes minimum if non-null.
`KeyCertificate(Certificate cert)` Up-convert a cert to this class
`KeyCertificate(SigningPublicKey spk)` A KeyCertificate with crypto type 0 (ElGamal) and the signature type and extra data from the given public key.
`KeyCertificate(SigningPublicKey spk, PublicKey pk)` A KeyCertificate with enc type from the given public key, and the signature type and extra data from the given public key.
`KeyCertificate(SigType type)` A KeyCertificate with crypto type 0 (ElGamal) and the signature type as specified.
`KeyCertificate(SigType type, EncType etype)` A KeyCertificate with crypto type and the signature type as specified.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`int`	`getCryptoTypeCode()` Gets the crypto type code from the certificate.
`EncType`	`getEncType()` Gets the encryption type from the certificate.
`byte[]`	`getExtraKeyData()` Signing Key extra data, if any, is first in the array.
`byte[]`	`getExtraSigningKeyData()` Signing Key extra data, if any.
`SigType`	`getSigType()` Gets the signature type from the certificate.
`int`	`getSigTypeCode()` Gets the signature type code from the certificate.
`KeyCertificate`	`toKeyCertificate()` Returns this certificate as a KeyCertificate.
`String`	`toString()` Returns a string representation of this KeyCertificate.

Methods inherited from class net.i2p.data.Certificate
create, create, equals, getCertificateType, getPayload, hashCode, readBytes, readBytes, setCertificateType, setPayload, size, writeBytes, writeBytes

Methods inherited from class net.i2p.data.DataStructureImpl
calculateHash, fromBase64, fromByteArray, read, toBase64, toByteArray

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- Field Detail
  - ECDSA256_PAYLOAD
```
static final byte[] ECDSA256_PAYLOAD
```
    ElG + P256
  - Ed25519_PAYLOAD
```
static final byte[] Ed25519_PAYLOAD
```
    ElG + Ed25519
  - ELG_ECDSA256_CERT
```
public static final KeyCertificate ELG_ECDSA256_CERT
```
    An immutable ElG/ECDSA-P256 certificate.
  - ELG_Ed25519_CERT
```
public static final KeyCertificate ELG_Ed25519_CERT
```
    An immutable ElG/Ed25519 certificate.
  - HEADER_LENGTH
```
public static final int HEADER_LENGTH
```
    Key certificate header length in bytes.
    See Also:
    Constant Field Values
  - X25519_Ed25519_CERT
```
public static final KeyCertificate X25519_Ed25519_CERT
```
    An immutable X25519/Ed25519 certificate.
  - X25519_Ed25519_PAYLOAD
```
static final byte[] X25519_Ed25519_PAYLOAD
```
    X25519 + Ed25519
- Constructor Detail
  - KeyCertificate
```
public KeyCertificate(byte[] payload)
               throws DataFormatException
```
    4 bytes minimum if non-null.
    Parameters:
    payload - 4 bytes minimum if non-null
    Throws:
    DataFormatException - if payload is too short
  - KeyCertificate
```
public KeyCertificate(Certificate cert)
               throws DataFormatException
```
    Up-convert a cert to this class
    Parameters:
    cert - payload 4 bytes minimum if non-null
    Throws:
    DataFormatException - if cert type != CERTIFICATE_TYPE_KEY
  - KeyCertificate
```
public KeyCertificate(SigningPublicKey spk)
```
    A KeyCertificate with crypto type 0 (ElGamal) and the signature type and extra data from the given public key.
    Parameters:
    spk - non-null data non-null
    Throws:
    IllegalArgumentException - if spk or spk data is null
  - KeyCertificate
```
public KeyCertificate(SigningPublicKey spk,
                      PublicKey pk)
```
    A KeyCertificate with enc type from the given public key, and the signature type and extra data from the given public key. EncType lengths greater than 256 not supported.
    Parameters:
    spk - non-null data non-null
    pk - non-null
    Throws:
    IllegalArgumentException - if spk, pk, or their data is null
  - KeyCertificate
```
public KeyCertificate(SigType type)
```
    A KeyCertificate with crypto type 0 (ElGamal) and the signature type as specified. Payload is created. If type.getPubkeyLen() is greater than 128, caller MUST fill in the extra key data in the payload.
    Parameters:
    type - non-null
    Throws:
    IllegalArgumentException - if type is null
  - KeyCertificate
```
public KeyCertificate(SigType type,
                      EncType etype)
```
    A KeyCertificate with crypto type and the signature type as specified. Payload is created. If type.getPubkeyLen() is greater than 128, caller MUST fill in the extra key data in the payload. EncType lengths greater than 256 not supported.
    Parameters:
    type - non-null
    etype - non-null
    Throws:
    IllegalArgumentException - if type or etype is null
- Method Detail
  - getCryptoTypeCode
```
public int getCryptoTypeCode()
```
    Gets the crypto type code from the certificate.
    Returns:
    -1 if unset
  - getEncType
```
public EncType getEncType()
```
    Gets the encryption type from the certificate.
    Returns:
    null if unset or unknown
  - getExtraKeyData
```
public byte[] getExtraKeyData()
```
    Signing Key extra data, if any, is first in the array. Crypto Key extra data, if any, is second in the array, at offset max(0, getSigType().getPubkeyLen() - 128)
    Returns:
    null if unset or none
  - getExtraSigningKeyData
```
public byte[] getExtraSigningKeyData()
```
    Signing Key extra data, if any.
    Returns:
    null if unset or none
    Throws:
    UnsupportedOperationException - if the sig type is unsupported
  - getSigType
```
public SigType getSigType()
```
    Gets the signature type from the certificate.
    Returns:
    null if unset or unknown
  - getSigTypeCode
```
public int getSigTypeCode()
```
    Gets the signature type code from the certificate.
    Returns:
    -1 if unset
  - toKeyCertificate
```
public KeyCertificate toKeyCertificate()
```
    Returns this certificate as a KeyCertificate.
    Overrides:
    toKeyCertificate in class Certificate
    Returns:
    the KeyCertificate
  - toString
```
public String toString()
```
    Returns a string representation of this KeyCertificate.
    Overrides:
    toString in class Certificate

Class KeyCertificate

Field Summary

Fields inherited from class net.i2p.data.Certificate

Constructor Summary

Method Summary

Methods inherited from class net.i2p.data.Certificate

Methods inherited from class net.i2p.data.DataStructureImpl

Methods inherited from class java.lang.Object

Field Detail

ECDSA256_PAYLOAD

Ed25519_PAYLOAD

ELG_ECDSA256_CERT

ELG_Ed25519_CERT

HEADER_LENGTH

X25519_Ed25519_CERT

X25519_Ed25519_PAYLOAD

Constructor Detail

KeyCertificate

KeyCertificate

KeyCertificate

KeyCertificate

KeyCertificate

KeyCertificate

Method Detail

getCryptoTypeCode

getEncType

getExtraKeyData

getExtraSigningKeyData

getSigType

getSigTypeCode

toKeyCertificate

toString