Certificate (Javadocs [I2P+ 2.13.0+]

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

All Implemented Interfaces:
Serializable, DataStructure
Direct Known Subclasses:
KeyCertificate
```
public class Certificate
extends DataStructureImpl
```
Extensible certificate system for I2P structures providing metadata and capabilities.
Certificate offers flexible metadata attachment to I2P identities:
- Metadata: Additional information beyond cryptographic keys
- DoS Protection: Help manage denial of service attacks
- Network Utilization: Control resource usage and capabilities
- Extensible: Support for multiple certificate types and formats
- Optional: Structures can have NULL certificates for minimal overhead
Supported Certificate Types:
- CERTIFICATE_TYPE_NULL - No certificate (default)
- CERTIFICATE_TYPE_HIDDEN - Service should not be published
- CERTIFICATE_TYPE_SIGNED - Signed by certificate authority
- CERTIFICATE_TYPE_MULTIPLE - Contains multiple certificates
- CERTIFICATE_TYPE_KEY - Specifies key types (KeyCertificate)
Common Use Cases:
- Identity Verification: Prove authenticity of routers/destinations
- Capability Advertising: Announce supported features and protocols
- Access Control: Specify service restrictions or requirements
- Resource Management: Indicate bandwidth or usage limitations
- Trust Establishment: Certificate authority-based trust chains
Security Considerations:
- Anonymous Network: CA-based certificates may not be appropriate
- Signature Verification: Always verify certificate signatures
- Trust Validation: Carefully evaluate certificate authorities
- Privacy Impact: Consider anonymity implications of certificates
Implementation Notes:
- Multiple Certificates: Support for multiple certificates is planned
- Size Efficiency: Minimal overhead for NULL certificates
- Flexibility: Payload can contain arbitrary metadata
- Backward Compatibility: Existing formats continue to be supported
Related Structures:
- Destination - Uses certificates for service identity
- RouterIdentity - Router certificates
- KeyCertificate - Specialized certificate for key type specification
See Also:
Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`protected byte[]`	`_payload` Certificate payload data
`protected int`	`_type` Certificate type identifier
`static int`	`CERTIFICATE_LENGTH_SIGNED_WITH_HASH` Length of signed certificate with hash (signature + hash)
`static int`	`CERTIFICATE_TYPE_HIDDEN` we should not be used for anything (don't use us in the netDb, in tunnels, or tell others about us)
`static int`	`CERTIFICATE_TYPE_KEY` Key certificate type.
`static int`	`CERTIFICATE_TYPE_MULTIPLE` Contains multiple certs
`static int`	`CERTIFICATE_TYPE_NULL` Specifies a null certificate type with no payload
`static int`	`CERTIFICATE_TYPE_SIGNED` Signed with 40-byte Signature and (optional) 32-byte hash
`static Certificate`	`NULL_CERT` Null certificate singleton

Constructor Summary
Constructors
Constructor and Description
Certificate()
Creates a new Certificate with default values.
Certificate(int type, byte[] payload)
Construct a certificate with the given type and payload.

Constructors
Constructor and Description
`Certificate()` Creates a new Certificate with default values.
`Certificate(int type, byte[] payload)` Construct a certificate with the given type and payload.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`static Certificate`	`create(byte[] data, int off)` If null, P256 key, or Ed25519 key cert, return immutable static instance, else create new
`static Certificate`	`create(InputStream in)` If null, P256 key, or Ed25519 key cert, return immutable static instance, else create new
`boolean`	`equals(Object object)`
`int`	`getCertificateType()` Certificate type.
`byte[]`	`getPayload()` Certificate payload, or null.
`int`	`hashCode()`
`int`	`readBytes(byte[] source, int offset)` Reads the certificate from the source array.
`void`	`readBytes(InputStream in)` Reads the certificate from an input stream.
`void`	`setCertificateType(int type)` Certificate type to set.
`void`	`setPayload(byte[] payload)` Certificate payload to set.
`int`	`size()` Serialized size in bytes.
`KeyCertificate`	`toKeyCertificate()` Up-convert this to a KeyCertificate
`String`	`toString()`
`int`	`writeBytes(byte[] target, int offset)` Writes the certificate to the target array.
`void`	`writeBytes(OutputStream out)` Write out the data structure to the stream, using the format defined in the I2P data structure specification.

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
  - _payload
```
protected byte[] _payload
```
    Certificate payload data
  - _type
```
protected int _type
```
    Certificate type identifier
  - CERTIFICATE_LENGTH_SIGNED_WITH_HASH
```
public static final int CERTIFICATE_LENGTH_SIGNED_WITH_HASH
```
    Length of signed certificate with hash (signature + hash)
  - CERTIFICATE_TYPE_HIDDEN
```
public static final int CERTIFICATE_TYPE_HIDDEN
```
    we should not be used for anything (don't use us in the netDb, in tunnels, or tell others about us)
    See Also:
    Constant Field Values
  - CERTIFICATE_TYPE_KEY
```
public static final int CERTIFICATE_TYPE_KEY
```
    Key certificate type.
    See Also:
    Constant Field Values
  - CERTIFICATE_TYPE_MULTIPLE
```
public static final int CERTIFICATE_TYPE_MULTIPLE
```
    Contains multiple certs
    See Also:
    Constant Field Values
  - CERTIFICATE_TYPE_NULL
```
public static final int CERTIFICATE_TYPE_NULL
```
    Specifies a null certificate type with no payload
    See Also:
    Constant Field Values
  - CERTIFICATE_TYPE_SIGNED
```
public static final int CERTIFICATE_TYPE_SIGNED
```
    Signed with 40-byte Signature and (optional) 32-byte hash
    See Also:
    Constant Field Values
  - NULL_CERT
```
public static final Certificate NULL_CERT
```
    Null certificate singleton
- Constructor Detail
  - Certificate
```
public Certificate()
```
    Creates a new Certificate with default values.
  - Certificate
```
public Certificate(int type,
                   byte[] payload)
```
    Construct a certificate with the given type and payload.
    Parameters:
    type - the certificate type
    payload - the certificate payload (may be null)
    Throws:
    IllegalArgumentException - if type < 0
- Method Detail
  - create
```
public static Certificate create(byte[] data,
                                 int off)
                          throws DataFormatException
```
    If null, P256 key, or Ed25519 key cert, return immutable static instance, else create new
    Parameters:
    data - the source data
    off - the offset into data
    Returns:
    the Certificate instance
    Throws:
    DataFormatException - if not enough bytes
  - create
```
public static Certificate create(InputStream in)
                          throws DataFormatException,
                                 IOException
```
    If null, P256 key, or Ed25519 key cert, return immutable static instance, else create new
    Parameters:
    in - the input stream
    Returns:
    the Certificate instance
    Throws:
    DataFormatException - if the data is malformed
    IOException - if there is an I/O error
  - equals
```
public boolean equals(Object object)
```
    Overrides:
    equals in class Object
  - getCertificateType
```
public int getCertificateType()
```
    Certificate type.
    Returns:
    the certificate type
  - getPayload
```
public byte[] getPayload()
```
    Certificate payload, or null.
    Returns:
    the certificate payload, or null
  - hashCode
```
public int hashCode()
```
    Overrides:
    hashCode in class Object
  - readBytes
```
public int readBytes(byte[] source,
                     int offset)
              throws DataFormatException
```
    Reads the certificate from the source array.
    Parameters:
    source - the source
    offset - the starting offset in the source
    Returns:
    the bytes consumed
    Throws:
    IllegalStateException - if already set
    DataFormatException - if the data is malformed
  - readBytes
```
public void readBytes(InputStream in)
               throws DataFormatException,
                      IOException
```
    Reads the certificate from an input stream.
    Parameters:
    in - stream to read from
    Throws:
    IllegalStateException - if already set
    DataFormatException - if the data is improperly formatted
    IOException - if there was a problem reading the stream
  - setCertificateType
```
public void setCertificateType(int type)
```
    Certificate type to set.
    Parameters:
    type - the certificate type to set
    Throws:
    IllegalArgumentException - if type < 0
    IllegalStateException - if already set
  - setPayload
```
public void setPayload(byte[] payload)
```
    Certificate payload to set.
    Parameters:
    payload - the payload to set
    Throws:
    IllegalStateException - if already set
  - size
```
public int size()
```
    Serialized size in bytes.
    Returns:
    the serialized size in bytes
  - toKeyCertificate
```
public KeyCertificate toKeyCertificate()
                                throws DataFormatException
```
    Up-convert this to a KeyCertificate
    Returns:
    the KeyCertificate
    Throws:
    DataFormatException - if cert type != CERTIFICATE_TYPE_KEY
  - toString
```
public String toString()
```
    Overrides:
    toString in class Object
  - writeBytes
```
public int writeBytes(byte[] target,
                      int offset)
```
    Writes the certificate to the target array.
    Parameters:
    target - the output array
    offset - the starting offset in the target
    Returns:
    the written length (NOT the new offset)
  - writeBytes
```
public void writeBytes(OutputStream out)
                throws DataFormatException,
                       IOException
```
    Description copied from interface: DataStructure
    Write out the data structure to the stream, using the format defined in the I2P data structure specification.
    Parameters:
    out - stream to write to
    Throws:
    DataFormatException - if the data was incomplete or not yet ready to be written
    IOException - if there was a problem writing to the stream

Class Certificate

Field Summary

Constructor Summary

Method Summary

Methods inherited from class net.i2p.data.DataStructureImpl

Methods inherited from class java.lang.Object

Field Detail

_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 Detail

Certificate

Certificate

Method Detail

create

create

equals

getCertificateType

getPayload

hashCode

readBytes

readBytes

setCertificateType

setPayload

size

toKeyCertificate

toString

writeBytes

writeBytes