com.macasaet.fernet.Token Maven / Gradle / Ivy
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/**
Copyright 2017 Carlos Macasaet
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package com.macasaet.fernet;
import static com.macasaet.fernet.Constants.charset;
import static com.macasaet.fernet.Constants.cipherTextBlockSize;
import static com.macasaet.fernet.Constants.decoder;
import static com.macasaet.fernet.Constants.encoder;
import static com.macasaet.fernet.Constants.initializationVectorBytes;
import static com.macasaet.fernet.Constants.minimumTokenBytes;
import static com.macasaet.fernet.Constants.signatureBytes;
import static com.macasaet.fernet.Constants.supportedVersion;
import static com.macasaet.fernet.Constants.tokenStaticBytes;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.time.Instant;
import java.util.Base64.Encoder;
import java.util.Collection;
import javax.crypto.spec.IvParameterSpec;
/**
* A Fernet token.
*
* Copyright © 2017 Carlos Macasaet.
*
* @author Carlos Macasaet
*/
@SuppressWarnings({"PMD.TooManyMethods", "PMD.AvoidDuplicateLiterals"})
/*
* TooManyMethods can be avoided by making the following API-breaking changes:
* * remove the static `generate` methods and introduce a `TokenFactory` or `TokenBuilder`
* * remove the public `validateAndDecrypt` methods since they are already available in the `Validator` interface
*
* AvoidDuplicateLiterals is from the method-level @SuppressWarnings annotations
*/
public class Token {
private final byte version;
private final Instant timestamp;
private final IvParameterSpec initializationVector;
private final byte[] cipherText;
private final byte[] hmac;
/**
* Initialise a new Token from raw components. No validation of the signature is performed. However, the other
* fields are validated to ensure they conform to the Fernet specification.
*
* Warning: Subsequent modifications to the input arrays will write through to this object.
*
* @param version
* The version of the Fernet token specification. Currently, only 0x80 is supported.
* @param timestamp
* the time the token was generated
* @param initializationVector
* the randomly-generated bytes used to initialise the encryption cipher
* @param cipherText
* the encrypted the encrypted payload
* @param hmac
* the signature of the token
*/
@SuppressWarnings({"PMD.ArrayIsStoredDirectly", "PMD.CyclomaticComplexity"})
protected Token(final byte version, final Instant timestamp, final IvParameterSpec initializationVector,
final byte[] cipherText, final byte[] hmac) {
if (version != supportedVersion) {
throw new IllegalTokenException("Unsupported version: " + version);
}
if (timestamp == null) {
throw new IllegalTokenException("timestamp cannot be null");
}
if (initializationVector == null || initializationVector.getIV().length != initializationVectorBytes) {
throw new IllegalTokenException("Initialization Vector must be 128 bits");
}
if (cipherText == null || cipherText.length % cipherTextBlockSize != 0) {
throw new IllegalTokenException("Ciphertext must be a multiple of 128 bits");
}
if (hmac == null || hmac.length != signatureBytes) {
throw new IllegalTokenException("hmac must be 256 bits");
}
this.version = version;
this.timestamp = timestamp;
this.initializationVector = initializationVector;
this.cipherText = cipherText;
this.hmac = hmac;
}
/**
* Read a Token from bytes. This does NOT validate that the token was
* generated using a valid {@link Key}.
*
* @param bytes a Fernet token in the form Version | Timestamp | IV |
* Ciphertext | HMAC
* @return a new Token
* @throws IllegalTokenException if the input string cannot be a valid
* token irrespective of key or timestamp.
*/
@SuppressWarnings({"PMD.PrematureDeclaration", "PMD.DataflowAnomalyAnalysis"})
public static Token fromBytes(final byte[] bytes) {
if (bytes.length < minimumTokenBytes) {
throw new IllegalTokenException("Not enough bits to generate a Token");
}
try (ByteArrayInputStream inputStream = new ByteArrayInputStream(bytes)) {
try (DataInputStream dataStream = new DataInputStream(inputStream)) {
final byte version = dataStream.readByte();
final long timestampSeconds = dataStream.readLong();
final byte[] initializationVector = read(dataStream, initializationVectorBytes);
final byte[] cipherText = read(dataStream, bytes.length - tokenStaticBytes);
final byte[] hmac = read(dataStream, signatureBytes);
if (dataStream.read() != -1) {
throw new IllegalTokenException("more bits found");
}
return new Token(version, Instant.ofEpochSecond(timestampSeconds),
new IvParameterSpec(initializationVector), cipherText, hmac);
}
} catch (final IOException ioe) {
// this should not happen as I/O is from memory and stream
// length is verified ahead of time
throw new IllegalStateException(ioe.getMessage(), ioe);
}
}
protected static byte[] read(final DataInputStream stream, final int numBytes) throws IOException {
final byte[] retval = new byte[numBytes];
final int bytesRead = stream.read(retval);
if (bytesRead < numBytes) {
throw new IllegalTokenException("Not enough bits to generate a Token");
}
return retval;
}
/**
* Deserialise a Base64 URL Fernet token string. This does NOT validate that the token was generated using a valid {@link Key}.
*
* @param string
* the Base 64 URL encoding of a token in the form Version | Timestamp | IV | Ciphertext | HMAC
* @return a new Token
* @throws IllegalTokenException
* if the input string cannot be a valid token irrespective of key or timestamp
*/
public static Token fromString(final String string) {
return fromBytes(decoder.decode(string));
}
/**
* Convenience method to generate a new Fernet token with a string payload.
*
* @param key the secret key for encrypting plainText and signing the token
* @param plainText the payload to embed in the token
* @return a unique Fernet token
*/
public static Token generate(final Key key, final String plainText) {
return generate(new SecureRandom(), key, plainText);
}
/**
* Convenience method to generate a new Fernet token with a string payload.
*
* @param random a source of entropy for your application
* @param key the secret key for encrypting plainText and signing the token
* @param plainText the payload to embed in the token
* @return a unique Fernet token
*/
public static Token generate(final SecureRandom random, final Key key, final String plainText) {
return generate(random, key, plainText.getBytes(charset));
}
/**
* Convenience method to generate a new Fernet token.
*
* @param key the secret key for encrypting payload and signing the token
* @param payload the unencrypted data to embed in the token
* @return a unique Fernet token
*/
public static Token generate(final Key key, final byte[] payload) {
return generate(new SecureRandom(), key, payload);
}
/**
* Generate a new Fernet token.
*
* @param random a source of entropy for your application
* @param key the secret key for encrypting payload and signing the token
* @param payload the unencrypted data to embed in the token
* @return a unique Fernet token
*/
public static Token generate(final SecureRandom random, final Key key, final byte[] payload) {
final IvParameterSpec initializationVector = generateInitializationVector(random);
final byte[] cipherText = key.encrypt(payload, initializationVector);
final Instant timestamp = Instant.now();
final byte[] hmac = key.sign(supportedVersion, timestamp, initializationVector, cipherText);
return new Token(supportedVersion, timestamp, initializationVector, cipherText, hmac);
}
/**
* Check the validity of this token.
*
* @param key the secret key against which to validate the token
* @param validator an object that encapsulates the validation parameters (e.g. TTL)
* @return the decrypted, deserialised payload of this token
* @throws TokenValidationException if key was NOT used to generate this token
*/
@SuppressWarnings("PMD.LawOfDemeter")
public T validateAndDecrypt(final Key key, final Validator validator) {
return validator.validateAndDecrypt(key, this);
}
/**
* Check the validity of this token against a collection of keys. Use this if you have implemented key rotation.
*
* @param keys the active keys which may have been used to generate token
* @param validator an object that encapsulates the validation parameters (e.g. TTL)
* @return the decrypted, deserialised payload of this token
* @throws TokenValidationException if none of the keys were used to generate this token
*/
@SuppressWarnings("PMD.LawOfDemeter")
public T validateAndDecrypt(final Collection keys, final Validator validator) {
return validator.validateAndDecrypt(keys, this);
}
@SuppressWarnings({"PMD.ConfusingTernary", "PMD.LawOfDemeter"})
protected byte[] validateAndDecrypt(final Key key, final Instant earliestValidInstant,
final Instant latestValidInstant) {
if (getVersion() != (byte) 0x80) {
throw new TokenValidationException("Invalid version");
} else if (!getTimestamp().isAfter(earliestValidInstant)) {
throw new TokenExpiredException("Token is expired");
} else if (!getTimestamp().isBefore(latestValidInstant)) {
throw new TokenValidationException("Token timestamp is in the future (clock skew).");
} else if (!isValidSignature(key)) {
throw new TokenValidationException("Signature does not match.");
}
return key.decrypt(getCipherText(), getInitializationVector());
}
/**
* @return the Base 64 URL encoding of this token in the form Version | Timestamp | IV | Ciphertext | HMAC
*/
@SuppressWarnings("PMD.LawOfDemeter")
public String serialise() {
try (ByteArrayOutputStream byteStream = new ByteArrayOutputStream(
tokenStaticBytes + getCipherText().length)) {
writeTo(byteStream);
return getEncoder().encodeToString(byteStream.toByteArray());
} catch (final IOException e) {
// this should not happen as IO is to memory only
throw new IllegalStateException(e.getMessage(), e);
}
}
/**
* Write the raw bytes of this token to the specified output stream.
*
* @param outputStream
* the target
* @throws IOException
* if data cannot be written to the underlying stream
*/
@SuppressWarnings("PMD.LawOfDemeter")
public void writeTo(final OutputStream outputStream) throws IOException {
try (DataOutputStream dataStream = new DataOutputStream(outputStream)) {
dataStream.writeByte(getVersion());
dataStream.writeLong(getTimestamp().getEpochSecond());
dataStream.write(getInitializationVector().getIV());
dataStream.write(getCipherText());
dataStream.write(getHmac());
}
}
/**
* @return the Fernet specification version of this token
*/
public byte getVersion() {
return version;
}
/**
* @return the time that this token was generated
*/
public Instant getTimestamp() {
return timestamp;
}
/**
* @return the initialisation vector used to encrypt the token contents
*/
public IvParameterSpec getInitializationVector() {
return initializationVector;
}
public String toString() {
final StringBuilder builder = new StringBuilder(107);
builder.append("Token [version=").append(String.format("0x%x", new BigInteger(1, new byte[] {getVersion()})))
.append(", timestamp=").append(getTimestamp())
.append(", hmac=").append(encoder.encodeToString(getHmac())).append(']');
return builder.toString();
}
protected static IvParameterSpec generateInitializationVector(final SecureRandom random) {
return new IvParameterSpec(generateInitializationVectorBytes(random));
}
protected static byte[] generateInitializationVectorBytes(final SecureRandom random) {
final byte[] retval = new byte[initializationVectorBytes];
random.nextBytes(retval);
return retval;
}
/**
* Recompute the HMAC signature of the token with the stored shared secret key.
*
* @param key
* the shared secret key against which to validate the token
* @return true if and only if the signature on the token was generated using the supplied key
*/
public boolean isValidSignature(final Key key) {
final byte[] computedHmac = key.sign(getVersion(), getTimestamp(), getInitializationVector(),
getCipherText());
return MessageDigest.isEqual(getHmac(), computedHmac);
}
protected Encoder getEncoder() {
return encoder;
}
/**
* Warning: modifications to the returned array will write through to this object.
*
* @return the raw encrypted payload bytes
*/
@SuppressWarnings("PMD.MethodReturnsInternalArray")
protected byte[] getCipherText() {
return cipherText;
}
/**
* Warning: modifications to the returned array will write through to this object.
*
* @return the HMAC 256 signature of this token
*/
@SuppressWarnings("PMD.MethodReturnsInternalArray")
protected byte[] getHmac() {
return hmac;
}
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