iaik.security.rsa
Class RSASignature

java.lang.Object
  |
  +--java.security.SignatureSpi
        |
        +--java.security.Signature
              |
              +--iaik.security.rsa.RSASignature

Direct Known Subclasses:

Md2RSASignature, Md5RSASignature, ShaRSASignature

public abstract class RSASignature

extends Signature

This class extends the java.security.Signature class for providing the functionality of the RSA digital signature algorithm, featured by any proper hash algorithm.

Within the IAIK-JCE environment, this class is extended by Md2RSASignature, Md5RSASignature, ShaRSASignature and SSLRSASignature for supporting the "MD2 with RSA", "MD5 with RSA" (as described in PKCS#1) and "SHA with RSA" signature algorithms, and a particular signature scheme to be used within the Secure Sockets Layer SSLv3 protocol.

Digital signatures are used for ensuring data authentication and data integrity. RSA based signature algorithms use a proper hash function (like MD2, MD5 or SHA) for creating a message digest of the message to be signed. Subsequently this message digest is encrypted with the RSA private key of the entity going to sign the message. Message and encrypted message digest together are sent to the intended receiver that verifies the signature by decrypting the received encrypted message digest with the corresponding RSA public key, and comparing it with the hash value derived from the received original message after hashing it with the same hash function as used by the entity that has sent the message.

This class follows the guidelines presented in PKCS#1) for implementing a signature algorithm based on the RSA encryption method for being used in signing X.509/PEM certificates, certificate-revocation lists, PKCS#6 extended certificates, and other objects employing digital signatures such as X.401 message tokens. The algorithms presented in PKCS#1 are not intended to be used in PKCS#7, where signatures (encrypted message digests) are treated as octet strings, in contrast to the bit string interpretation of PKCS#1.

For implementing a RSASignature with a specific hash algorithm you only have to extend this class and supply the variable "hash" with an instance of the desired hash algorithm, see Md2RSASignature, Md5RSASignature, ShaRSASignature.

An application wishing to sign some message or to verify some signature, generally has to perform three steps (in the following example, HASH has to be replaced by the name of the desired hash algorithm):

• First an instance of the desired signature algorithm has to be created using a proper getInstance method, e.g.:

   Signature hash_rsa = Signature.getInstance("HASH/RSA");
   

• Second, the Signature object just created has to be properly initialized for signing a message respectively verifying a signature using a RSA private respectively RSA public key, e.g.:
  • Initialize for Signing: hash_rsa.initSign(rsaPrivateKey);
  • Initialize for Verifying: hash_rsa.initVerify(rsaPublicKey);

• Finally, if the Signature object has been initialized for signing, the data to be signed is supplied to it and subsequently the signature is created by calling the sign method returning the signature as DER encoded byte array. Otherwise, if the Signature object has been initialized for verifying, first the data to be verified is supplied to the Signature object, and subsequently the signature is verified by calling the verify method, supplied with the DER encoded byte array holding the corresponding signature:
  • Supply the data to be signed, and subsequently sign it:

     hash_rsa.update(data);
     byte[] signature = hash_rsa.sign();
     

  • Supply the data to be verified, and verify the signature:

     hash_rsa.update(data);
     System.out.println("Signature " + (hash_rsa.verify(signature) ? "correct!" : "not correct!"));
     

See Also:

Md2RSASignature, Md5RSASignature, ShaRSASignature, SSLRSASignature, Signature

Field Summary

protected MessageDigest

hash The MessageDigest used to hash the data; supplied with an instance of the desired MessageDigest algorithm by any extending subclass.

Fields inherited from class java.security.Signature

SIGN, state, UNINITIALIZED, VERIFY

Fields inherited from class java.security.SignatureSpi

appRandom

Constructor Summary

protected

RSASignature(AlgorithmID algorithm, MessageDigest hash) Creates a RSA Signature object with a specified hash algorithm.

Method Summary

protected java.lang.Object	engineGetParameter(java.lang.String param) This method is not implemented and only throws an InvalidParameterException
protected void	engineInitSign(PrivateKey pk) SPI: Initializes this Signature object with the given RSA private key for going to sign some data.
protected void	engineInitVerify(PublicKey pk) SPI: Initializes this Signature object with the given RSA public key for performing a signature verification.
protected void	engineSetParameter(java.lang.String param, java.lang.Object value) This method is not implemented and only throws an InvalidParameterException
protected byte[]	engineSign() SPI: Returns a byte array holding the signature resulting from all already performed data update operations.
protected void	engineUpdate(byte b) SPI: Updates the data to be signed or verified with the specified byte.
protected void	engineUpdate(byte[] b, int off, int len) SPI: Updates the data to be signed or verified with the specified number of bytes, beginning at the specified offset within the given byte array.
protected boolean	engineVerify(byte[] sigBytes) Verifies the given signature of a message according to PKCS#1.

Methods inherited from class java.security.Signature

clone, getAlgorithm, getInstance, getInstance, getParameter, getProvider, initSign, initSign, initVerify, setParameter, setParameter, sign, sign, toString, update, update, update, verify

Methods inherited from class java.security.SignatureSpi

engineInitSign, engineSetParameter, engineSign

Methods inherited from class java.lang.Object

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

Field Detail

hash

protected MessageDigest hash

The MessageDigest used to hash the data; supplied with an instance of the desired MessageDigest algorithm by any extending subclass.

See Also:

Md2RSASignature, Md5RSASignature, ShaRSASignature

Constructor Detail

RSASignature

protected RSASignature(AlgorithmID algorithm,
                       MessageDigest hash)

Creates a RSA Signature object with a specified hash algorithm.

This constructor is called from subclasses to represent a RSA signature with a defined hash algorithm like Md2, Md5 or Sha.

Applications use

 Signature.getInstance("HASHwithRSA");
 

for creating a Signature object, where HASH has to be replaced by the name of the desired hash algorithm.

Parameters:

algorithm - the hash algorithm to use

See Also:

Md2RSASignature, Md5RSASignature, ShaRSASignature, Signature.getInstance(java.lang.String)

Method Detail

engineInitVerify

protected void engineInitVerify(PublicKey pk)
                         throws InvalidKeyException

SPI: Initializes this Signature object with the given RSA public key for performing a signature verification.

Overrides:

engineInitVerify in class SignatureSpi

Parameters:

publicKey - the RSA public key belonging to the RSA private key that has been used for signing.

Throws:

InvalidKeyException - if a key encoding error occurs

engineInitSign

protected void engineInitSign(PrivateKey pk)
                       throws InvalidKeyException

SPI: Initializes this Signature object with the given RSA private key for going to sign some data.

Overrides:

engineInitSign in class SignatureSpi

Parameters:

privateKey - the RSA private key to be used for signing.

Throws:

InvalidKeyException - if a key encoding error occurs

engineSign

protected byte[] engineSign()
                     throws SignatureException

SPI: Returns a byte array holding the signature resulting from all already performed data update operations.

The signature is returned as defined in PKCS#1, claiming for an ASN.1 BIT STRING object. For building the signature according to PKCS#1, the data resulting from the several update operations is digested using the defined message digest algorithm. Subsequently, from message digest and message-digest AlgorithmID an ASN.1 DigestInfo object is created and DER encoded as required by PKCS#1:

 DigestInfo ::= SEQUENCE {
    digestAlgorithm DigestAlgorithmIdentifier,
    digest Digest }
 
 DigestAlgorithmIdentifier ::= AlgorithmIdentifier
 Digest ::= OCTET STRING
 

Subsequently the RSA encryption is performed with the signer´s RSA private key and the resulting octet string is converted to the bit string yielding the desired PKCS#1 signature.

Overrides:

engineSign in class SignatureSpi

Returns:

a byte array holding the signature

Throws:

SignatureException - if an error occurs when creating the signature

engineVerify

protected boolean engineVerify(byte[] sigBytes)
                        throws SignatureException

Verifies the given signature of a message according to PKCS#1.

PKCS#1 defines a signature as bit string, which has to be converted into an octet string, RSA decrypted with the signer´s RSA public key, and DER decoded for giving an ASN.1 DigestInfo. From this DigestInfo the message digest shall be taken for comparing it with the message digest derived from hashing the original message with the same message digest algorithm.

Overrides:

engineVerify in class SignatureSpi

Parameters:

sigBytes - the signature bytes to be verified

Returns:

true if signature is OK, false otherwise

Throws:

SignatureException - if an error occurs when verifying the signature

engineUpdate

protected void engineUpdate(byte b)

SPI: Updates the data to be signed or verified with the specified byte.

Overrides:

engineUpdate in class SignatureSpi

Parameters:

b - the byte to be used for updating.

engineUpdate

protected void engineUpdate(byte[] b,
                            int off,
                            int len)

SPI: Updates the data to be signed or verified with the specified number of bytes, beginning at the specified offset within the given byte array.

Overrides:

engineUpdate in class SignatureSpi

Parameters:

b - the byte array holding the data to be used for this update operation.

off - the offset, indicating the start position within the given byte array.

len - the number of bytes to be obtained from the given byte array, starting at the given position.

engineSetParameter

protected void engineSetParameter(java.lang.String param,
                                  java.lang.Object value)
                           throws InvalidParameterException

This method is not implemented and only throws an InvalidParameterException

Overrides:

engineSetParameter in class SignatureSpi

Throws:

InvalidParameterException - This Method is not supported

engineGetParameter

protected java.lang.Object engineGetParameter(java.lang.String param)
                                       throws InvalidParameterException

This method is not implemented and only throws an InvalidParameterException

Overrides:

engineGetParameter in class SignatureSpi

Throws:

InvalidParameterException - This Method is not supported