java.lang.Object
net.i2p.data.DataStructureImpl
net.i2p.data.Certificate
net.i2p.data.KeyCertificate
All Implemented Interfaces:
Serializable, DataStructure
Direct Known Subclasses:
KeyCertificate.ECDSA256Cert, KeyCertificate.Ed25519Cert, KeyCertificate.X25519_Ed25519Cert
public class KeyCertificateextends 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:

  • Field Details

    • HEADER_LENGTH

      public static final int HEADER_LENGTH
      Key certificate header length in bytes.
      See Also:

    • EMPTY

      private static final byte[] EMPTY
      Shared result for the no-extra-data case. Zero-length arrays cannot be mutated, so a single instance may be handed to every caller.

    • Ed25519_PAYLOAD

      static final byte[] Ed25519_PAYLOAD
      ElG + Ed25519.

    • ECDSA256_PAYLOAD

      static final byte[] ECDSA256_PAYLOAD
      ElG + P256.

    • X25519_Ed25519_PAYLOAD

      static final byte[] X25519_Ed25519_PAYLOAD
      X25519 + 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.

    • X25519_Ed25519_CERT

      public static final KeyCertificate X25519_Ed25519_CERT
      An immutable X25519/Ed25519 certificate.

  • Constructor Details

    • 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(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

    • 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

  • Method Details

    • getSigTypeCode

      public int getSigTypeCode()
      Gets the signature type code from the certificate.
      Returns:
      -1 if unset

    • getCryptoTypeCode

      public int getCryptoTypeCode()
      Gets the crypto type code from the certificate.
      Returns:
      -1 if unset

    • getSigType

      public SigType getSigType()
      Gets the signature type from the certificate.
      Returns:
      null if unset or unknown

    • 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:
      empty array if unset or none

    • getExtraSigningKeyData

      public byte[] getExtraSigningKeyData()
      Signing Key extra data, if any.
      Returns:
      empty array if unset or none
      Throws:
      UnsupportedOperationException - if the sig type is unsupported

    • toKeyCertificate

      public KeyCertificate toKeyCertificate()
      Returns this certificate as a KeyCertificate.
      Overrides:
      toKeyCertificate in class Certificate
      Returns:
      a new KeyCertificate wrapping this certificate's payload

    • toString

      public String toString()
      Returns a string representation of this KeyCertificate.
      Overrides:
      toString in class Certificate