iaik.security.cipher

Class GCMParameters

java.lang.Object

java.security.AlgorithmParametersSpi

iaik.security.cipher.GCMParameters

public class GCMParameters
extends java.security.AlgorithmParametersSpi

This class represents GCM parameters. The parameters specified for the GCM algorithm in RFC 5084 consist of the nonce and the length of the MAC (ICVlen):

 GCMParameters ::= SEQUENCE {
       aes-nonce        OCTET STRING, -- recommended size is 12 octets
       aes-ICVlen       AES-GCM-ICVlen DEFAULT 12 }

 AES-GCM-ICVlen ::= INTEGER (12 | 13 | 14 | 15 | 16)
 

The aes-ICVLen specifies the length of the message authentication code value.

As stated in the NIST Special Publication 800-38D also the MAC length of 4 and 8 bytes are possible. Additionally, this class holds the GCM parameter associated data and MAC block.

GCMParameters can be generated by calling one of the AlgorithmParameters.getInstance methods. Subsequently, the new AlgorithmParameters object must be initialized with a proper parameter specification (class GCMParameterSpec is recommended) or a DER encoded byte array, e.g.

 GCMParameterSpec gcmParamSpec = ...;
 AlgorithmParameters params = AlgorithmParameters.getInstance("GCM", "IAIK");
 params.init(gcmParamsSpec);
 

The GCMParameters can also be initialized with an IvParameterSpec object. In this case, the specified IV will be used as nonce.

Version:

File Revision 4

See Also:

GCMParameterSpec, AlgorithmParametersSpi

Constructor Summary

Constructors

Constructor and Description
GCMParameters() The default constructor.
GCMParameters(byte[] aad, byte[] nonce, byte[] macBlock, int macLength) Creates GCM Parameters with the given additional data, IV, MAC length and MAC block.

Method Summary

Modifier and Type	Method and Description
static void	checkKeyAndNonceReuse(boolean check) Dis/Enables check for key/nonce reuse.
static void	disableJava7ApiSupport(boolean disable) Disables support for Java7 GCM API.
protected byte[]	engineGetEncoded() Returns the parameters as DER byte array.
protected byte[]	engineGetEncoded(java.lang.String format) Returns the parameters as a DER byte array.
protected java.security.spec.AlgorithmParameterSpec	engineGetParameterSpec(java.lang.Class paramSpec) Returns a GCM Parameter Specification of this GCM Parameters object.
protected void	engineInit(java.security.spec.AlgorithmParameterSpec paramSpec) Initializes this parameters object using the parameters specified in paramSpec.
protected void	engineInit(byte[] params) Initializes this GCMParameters object from the given DER encoded byte array.
protected void	engineInit(byte[] params, java.lang.String format) Inits the parameters from an DER encoded byte array.
protected java.lang.String	engineToString() Returns a formatted string describing the GCM Parameters.
static void	setIncludeDefaultMacLengthInEncding(boolean include) Decides whether the aes-ICVlen (macLength) component should be included when encoding GCM parameters if it has the default value (12).
static void	setUseJava7ApiByDefault(boolean useJava7Api) Decides whether to use the Java7 GCM API also when the Cipher has not been initialized with a javax.crypto.spec.GCMParameterSpec and no additional authenticated data (AAD) has been specified by Cipher.updateAAD() call(s).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GCMParameters

public GCMParameters()
              throws java.security.InvalidAlgorithmParameterException

The default constructor. No values are set for the parameters. Use AlgorithmParameters.getInstance for obtaining a GCMParameters object.

Throws:

java.security.InvalidAlgorithmParameterException - if the parameter values are incorrect

GCMParameters

public GCMParameters(byte[] aad,
                     byte[] nonce,
                     byte[] macBlock,
                     int macLength)
              throws java.security.InvalidAlgorithmParameterException

Creates GCM Parameters with the given additional data, IV, MAC length and MAC block.

Parameters:

aad - the additional data that is authenticated

nonce - the nonce to generate the IV

macLength - number of bytes used for authentication

macBlock - the authentication block

Throws:

java.security.InvalidAlgorithmParameterException - if the parameter values are incorrect

Method Detail

setIncludeDefaultMacLengthInEncding

public static void setIncludeDefaultMacLengthInEncding(boolean include)

Decides whether the aes-ICVlen (macLength) component should be included when encoding GCM parameters if it has the default value (12). Although default values should be not included (if DER is used) it might be required to include the default value for compatibility reasons (when BER is used).

Parameters:

include - whether to include a default macLength value (12) when encoding GCM parameters or not (by default the default value is not included)

disableJava7ApiSupport

public static void disableJava7ApiSupport(boolean disable)

Disables support for Java7 GCM API.

With the IAIK provider GCM maybe used in two alternative ways: with the IAIK GCM API (where an iaik.security.cipher.GCMParameterSpec object has to be used to specify any additional authenticated data (AAD) and the mac value is returned with the GCM parameters) or with the Java7 API (where the additional authenticated data (AAD) has to be specified by Cipher.updateAAD() call(s) and the mac value is appended to the cipher text). The IAIK provider (version 5.4 or later) supports both APIs, but when decrypting a cipher text the same API shall be used that has been used to create the create the cipher text, i.e. the API usages shall not be mixed.
By default (without specific initialization) the IAIK GCM API is used (with a default tag length value of 12 bytes and a random 12 byte nonce value). When initializing the Cipher with a javax.crypto.spec.GCMParameterSpec or using Cipher method updateAAD() to specify additional authenticated data (AAD) the IAIK GCM Cipher automatically switches to the Java7 GCM API (using a default tag length of 16 bytes and a default 12 byte nonce value) and appending the mac value to the cipher text.

With this disableJava7ApiSupport you can disable Java7 GCM API support to ensure to use only the IAIK GCM API. Alternatively Java7 GCM API support may be disabled by using the "iaikjce.disableJava7GCMApiSupport" system property, e.g.:

 java -Diaikjce.disableJava7GCMApiSupport=true MyGCMApp
 

Parameters:

disable - true to disable Java7 GCM API support, false (default) to enable Java7 GCM API support

setUseJava7ApiByDefault

public static void setUseJava7ApiByDefault(boolean useJava7Api)

Decides whether to use the Java7 GCM API also when the Cipher has not been initialized with a javax.crypto.spec.GCMParameterSpec and no additional authenticated data (AAD) has been specified by Cipher.updateAAD() call(s).

With the IAIK provider GCM maybe used in two alternative ways: with the IAIK GCM API (where an iaik.security.cipher.GCMParameterSpec object has to be used to specify any additional authenticated data (AAD) and the mac value is returned with the GCM parameters) or with the Java7 API (where the additional authenticated data (AAD) has to be specified by Cipher.updateAAD() call(s) and the mac value is appended to the cipher text). The IAIK provider (version 5.4 or later) supports both APIs, but when decrypting a cipher text the same API shall be used that has been used to create the create the cipher text, i.e. the API usages shall not be mixed.
By default (without specific initialization) the IAIK GCM API is used (with a default tag length value of 12 bytes and a random 12 byte nonce value). When initializing the Cipher with a javax.crypto.spec.GCMParameterSpec or using Cipher method updateAAD() to specify additional authenticated data (AAD) the IAIK GCM Cipher automatically switches to the Java7 GCM API (using a default tag length of 16 bytes and a default 12 byte nonce value) and appending the mac value to the cipher text. When calling this setUseJava7ApiByDefault method the Java7 GCM API is used by default (also when not initializing the Cipher with an AlgorithmParameterSpec or not calling updateAAD()<9.

Parameters:

useJava7Api - true to use the Java7 GCM API by default, false (default) to use the IAIK GCM API by default

checkKeyAndNonceReuse

public static void checkKeyAndNonceReuse(boolean check)

Dis/Enables check for key/nonce reuse.

GCM shall not be used with same key and nonce multiple times. We cannot check any key/nonce pair that may have been used in the past, but we can check if a Cipher has been reinitialized before used for encryption a second time. This means we only check if Cipher.init() has been called before any further Cipher.update() or Cipher.doFinal() after an encryption operation has been finished; we do not check if an Cipher.init() call has actually provided a new key/nonce combination.

Parameters:

check - true to enable key/nonce reuse check (default), false to disable it

engineGetEncoded

protected byte[] engineGetEncoded()
                           throws java.io.IOException

Returns the parameters as DER byte array.

Specified by:

engineGetEncoded in class java.security.AlgorithmParametersSpi

Returns:

the GCM parameters as DER byte array

Throws:

java.io.IOException - if an encoding error occurs

engineGetEncoded

protected byte[] engineGetEncoded(java.lang.String format)
                           throws java.io.IOException

Returns the parameters as a DER byte array.

Format is ignored. Only DER encoding is supported at this time. This method only calls engineGetEncoded(), regardless of what is specified in the format string.

Specified by:

engineGetEncoded in class java.security.AlgorithmParametersSpi

Parameters:

format - the encoding format; ignored

Returns:

the GCM parameters as DER byte array

Throws:

java.io.IOException - if an encoding error occurs

engineGetParameterSpec

protected java.security.spec.AlgorithmParameterSpec engineGetParameterSpec(java.lang.Class paramSpec)
                                                                    throws java.security.spec.InvalidParameterSpecException

Returns a GCM Parameter Specification of this GCM Parameters object. paramSpec identifies the specification class in which the parameters should be returned, which might be iaik.security.cipher.GCMParameterSpec or javax.crypto.spec.GCMParameterSpec. Since GCM support has not been been introduced before Java7 javax.crypto.spec.GCMParameterSpec can only be used with Java 7 or later.
The IAIK provider has supported GCM already before Java7. For that reason using GCM with the IAIK API differs from using GCM with the Java7 API. With the IAIK API the GCM parameters (iaik.security.cipher.GCMParameterSpec) have to be used to specify any additional authenticated data (AAD); the Java7 API has added the updateAAD method to the Cipher engine class for specifying additional authenticated data. The IAIK API returns the mac value with the GCM parameters, the Java7 API appends the mac value to the cipher text. For that reason the IAIK API and Java7 are not fully compatible (different parameters and AAD handling, different mac handling). For instance, when decrypting/verifiying an IAIK GCM encrypted message with the Java7 API the mac value has to be got from the GCMParameters and appended to the cipher text. For that reason IAIK API usage should not be mixed with Java7 API using.

However, the IAIK provider (version 5.4 or later) also supports the Java7 API when initializing the Cipher with javax.crypto.spec.GCMParameterSpec parameters and using method updateAAD for providing the additional authenticated data (AAD), e.g.:

 // the cipher key
 KeyGenerator kg = KeyGenerator.getInstance("AES", "IAIK");
 SecretKey key = kg.generateKey();
 
 // specify mac length (in bits) and nonce 
 int macLen = 128; 
 byte[] nonce = new byte[12];
 random.nextBytes(nonce);
 javax.crypto.spec.GCMParameterSpec paramSpec = new javax.crypto.spec.GCMParameterSpec(macLen, nonce);
     
 // create and init Cipher     
 Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "IAIK");
 c.init(Cipher.ENCRYPT_MODE, key, paramSpec);

 // specify any AAD 
 byte[] aad = ...;
 cipher.updateAAD(aad); 
 
 // encrypt
 byte[] plainText = ...;
 byte[] cipherText = cipher.doFinal(plainText); 
 

For decrypting the Cipher is initialized with same key and parameters and the AAD again has to be specified by calling updateAAD before calling any update or doFinal method:

 // create and init Cipher     
 Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "IAIK");
 c.init(Cipher.DECRYPT_MODE, key, paramSpec);

 // specify any AAD 
 byte[] aad = ...;
 cipher.updateAAD(aad); 
 
 // decrypt
 byte[] plainText = cipher.doFinal(cipherText); 
 

With the IAIK API the AAD value has to be specified via IAIK GCM parameters:

 // the cipher key
 KeyGenerator kg = KeyGenerator.getInstance("AES", "IAIK");
 SecretKey key = kg.generateKey();
 
 // specify mac length (in bytes), nonce and AAD 
 int macLen = 16; 
 byte[] nonce = new byte[12];
 random.nextBytes(nonce);
 byte[] aad = ...;
 iaik.security.cipher.GCMParameterSpec paramSpec =
   new iaik.security.cipher.GCMParameterSpec(aad, nonce, macLen);
     
 // create and init Cipher     
 Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "IAIK");
 c.init(Cipher.ENCRYPT_MODE, key, paramSpec);
 
 // encrypt
 byte[] plainText = ...;
 byte[] cipherText = cipher.doFinal(plainText);
 
 // get GCM parameters containing the MAC value
 AlgorithmParameters params = cipher.getParameters();    
 

For decrypting the Cipher is initialized with same key and the parameters (containing the mac value) got from the encryption Cipher object:

 // create and init Cipher     
 Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "IAIK");
 c.init(Cipher.DECRYPT_MODE, myKey, params);
 
 // decrypt
 byte[] plainText = cipher.doFinal(cipherText); 
 

If you want to be assure that only the IAIK GCM API is used (to do not mix the API usage) you can disable Java7 API support by calling method disableJava7APISupport:

 GCMParameters.disableJava7ApiSupport(true);
 

In this case method getParameterSpec will throw an InvalidParameterSpecException when trying to get a javax.crypto.spec.GCMParameterSpec.

Specified by:

engineGetParameterSpec in class java.security.AlgorithmParametersSpi

Parameters:

paramSpec - the specification class in which the parameters should be returned - has to be class iaik.security.cipher.GCMParameterSpec or (Java7 or later) class javax.crypto.spec.GCMParameterSpec

Returns:

the parameter specification.

Throws:

java.security.spec.InvalidParameterSpecException - if the requested parameter specification is inappropriate for this parameter object.

engineInit

protected void engineInit(java.security.spec.AlgorithmParameterSpec paramSpec)
                   throws java.security.spec.InvalidParameterSpecException

Initializes this parameters object using the parameters specified in paramSpec. paramSpec might specify class iaik.security.cipher.GCMParameterSpec or class javax.crypto.spec.GCMParameterSpec. Since GCM support has not been been introduced before Java7 javax.crypto.spec.GCMParameterSpec can only be used with Java 7 or later.
The IAIK provider has supported GCM already before Java7. For that reason using GCM with the IAIK API differs from using GCM with the Java7 API. With the IAIK API the GCM parameters (iaik.security.cipher.GCMParameterSpec) have to be used to specify any additional authenticated data (AAD); the Java7 API has added the updateAAD method to the Cipher engine class for specifying additional authenticated data. The IAIK API returns the mac value with the GCM parameters, the Java7 API appends the mac value to the cipher text. For that reason the IAIK API and Java7 are not fully compatible (different parameters and AAD handling, different mac handling). For instance, when decrypting/verifiying an IAIK GCM encrypted message with the Java7 API the mac value has to be got from the GCMParameters and appended to the cipher text. For that reason IAIK API usage should not be mixed with Java7 API using.

However, the IAIK provider (version 5.4 or later) also supports the Java7 API when initializing the Cipher with javax.crypto.spec.GCMParameterSpec parameters and using method updateAAD for providing the additional authenticated data (AAD), e.g.:

 // the cipher key
 KeyGenerator kg = KeyGenerator.getInstance("AES", "IAIK");
 SecretKey key = kg.generateKey();
 
 // specify mac length (in bits) and nonce 
 int macLen = 128; 
 byte[] nonce = new byte[12];
 random.nextBytes(nonce);
 javax.crypto.spec.GCMParameterSpec paramSpec = new javax.crypto.spec.GCMParameterSpec(macLen, nonce);
     
 // create and init Cipher     
 Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "IAIK");
 c.init(Cipher.ENCRYPT_MODE, key, paramSpec);

 // specify any AAD 
 byte[] aad = ...;
 cipher.updateAAD(aad); 
 
 // encrypt
 byte[] plainText = ...;
 byte[] cipherText = cipher.doFinal(plainText); 
 

For decrypting the Cipher is initialized with same key and parameters and the AAD again has to be specified by calling updateAAD before calling any update or doFinal method:

 // create and init Cipher     
 Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "IAIK");
 c.init(Cipher.DECRYPT_MODE, key, paramSpec);

 // specify any AAD 
 byte[] aad = ...;
 cipher.updateAAD(aad); 
 
 // decrypt
 byte[] plainText = cipher.doFinal(cipherText); 
 

With the IAIK API the AAD value has to be specified via IAIK GCM parameters:

 // the cipher key
 KeyGenerator kg = KeyGenerator.getInstance("AES", "IAIK");
 SecretKey key = kg.generateKey();
 
 // specify mac length (in bytes), nonce and AAD 
 int macLen = 16; 
 byte[] nonce = new byte[12];
 random.nextBytes(nonce);
 byte[] aad = ...;
 iaik.security.cipher.GCMParameterSpec paramSpec =
   new iaik.security.cipher.GCMParameterSpec(aad, nonce, macLen);
     
 // create and init Cipher     
 Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "IAIK");
 c.init(Cipher.ENCRYPT_MODE, key, paramSpec);
 
 // encrypt
 byte[] plainText = ...;
 byte[] cipherText = cipher.doFinal(plainText);
 
 // get GCM parameters containing the MAC value
 AlgorithmParameters params = cipher.getParameters();    
 

For decrypting the Cipher is initialized with same key and the parameters (containing the mac value) got from the encryption Cipher object:

 // create and init Cipher     
 Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "IAIK");
 c.init(Cipher.DECRYPT_MODE, myKey, params);
 
 // decrypt
 byte[] plainText = cipher.doFinal(cipherText); 
 

If you want to be assure that only the IAIK GCM API is used (to do not mix the API usage) you can disable Java7 API support by calling method disableJava7APISupport:

 GCMParameters.disableJava7ApiSupport(true);
 

In this case method init will throw an InvalidParameterSpecException when trying to init the GCM parameters with a javax.crypto.spec.GCMParameterSpec.

Specified by:

engineInit in class java.security.AlgorithmParametersSpi

Parameters:

paramSpec - the parameter specification - must be GCMParameterSpec.

Throws:

java.security.spec.InvalidParameterSpecException - if the given parameter specification is inappropriate for the initialization of this parameter object.

engineInit

protected void engineInit(byte[] params)
                   throws java.io.IOException

Initializes this GCMParameters object from the given DER encoded byte array.

Specified by:

engineInit in class java.security.AlgorithmParametersSpi

Parameters:

params - the DER encoded byte array

Throws:

java.io.IOException - if an error occurs when decoding the given byte array or the derived parameter values are invalid

engineInit

protected void engineInit(byte[] params,
                          java.lang.String format)
                   throws java.io.IOException

Inits the parameters from an DER encoded byte array. Format is ignored. Only calls {engineInit(params) for initializing this GCMParameters object from the given DER encoded byte array, regardless of what is specified in the format string.

Specified by:

engineInit in class java.security.AlgorithmParametersSpi

Parameters:

params - the DER encoded byte array

format - the encoding format; ignored

Throws:

java.io.IOException - if an error occurs when decoding the given byte array

engineToString

protected java.lang.String engineToString()

Returns a formatted string describing the GCM Parameters.

Specified by:

engineToString in class java.security.AlgorithmParametersSpi

Returns:

a formatted string describing the GCM Parameters.