Converting Secret Keys to and from Byte Arrays

This section provides a quick introduction of the SecretKeySpec class and the KeySpec interface. They can be used to convert secret keys into byte arrays to store them in external files.

Converting a secret key to a byte array is supported by the SecretKey interface with the getEncoded() method. All secret key implementation classes use the RAW encoding format.

Converting a secret key from a byte array is not so easy. Two options are available:

1. javax.crypto.spec.SecretKeySpec is a class represents a secret key in a generic fashion. It offers the following constructor and methods:

SecretKeySpec() - Convert a secret key from the specified byte array according to the specified algorithm and constructs a SecretKeySpec object based on the secret key.

getAlgorithm() - Returns the algorithm name used to generate the key.

getEncoded() - Returns the key as a byte array in its primary encoding format.

getFormat() - Returns the name of the primary encoding format of this key.

2. java.security.spec.KeySpec is an interface providing a grouping point for algorithm specific key specification implementations. There are two implementations for secret key algorithms:

javax.crypto.spec.DESKeySpec is a KeySpec implementation for DES algorithm. It offers DESKeySpec() to construct a KeySpec object from the specific byte array.

javax.crypto.spec.DESedeKeySpec is a KeySpec implementation for DESede algorithm. It offers DESedeKeySpec() to construct a KeySpec object from the specific byte array.

javax.crypto.spec.SecretKeyFactory is a class as a conversion tool between SecretKey objects and algorithm specific KeySpec objects. It offers the following methods:

getInstance() - Returns a SecretKeyFactory object of the specified algorithm and the specified security package provider. If not specified, the default security pacage provider will be used.

generateSecret() - Generates a SecretKey object from the specified KeySpec object, and returns it.

getKeySpec() - Converts a SecretKey object to a KeySpec object, and returns it.

getAlgorithm() - Returns the algorithm name of this object.

getProvider() - Returns the provider as a provider object of this object.

See the next section on how to use the SecretKeySpec class and the KeySpec interface in a sample program.

Last update: 2014.

Table of Contents

 About This JDK Tutorial Book

 Downloading and Installing JDK 1.8.0 on Windows

 Downloading and Installing JDK 1.7.0 on Windows

 Downloading and Installing JDK 1.6.2 on Windows

 Java Date-Time API

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 Message Digest Algorithm Implementations in JDK

 Private key and Public Key Pair Generation

 PKCS#8/X.509 Private/Public Encoding Standards

 Digital Signature Algorithm and Sample Program

 "keytool" Commands and "keystore" Files

 KeyStore and Certificate Classes

Secret Key Generation and Management

 javax.crypto.SecretKey - The Secret Key Interface

 javax.crypto.KeyGenerator - Generating Secret Keys

Converting Secret Keys to and from Byte Arrays

 JceSecretKeyTest.java - Secret Key Test Program

 Cipher - Secret Key Encryption and Decryption

 The SSL (Secure Socket Layer) Protocol

 SSL Socket Communication Testing Programs

 SSL Client Authentication

 HTTPS (Hypertext Transfer Protocol Secure)

 Outdated Tutorials

 References

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