iaik.pkcs.pkcs7
Class DigestInfo

java.lang.Object
  |
  +--iaik.pkcs.pkcs7.DigestInfo

All Implemented Interfaces:

ASN1Type

public class DigestInfo

extends Object

implements ASN1Type

This class implements the PKCS#7 DigestInfo type.

The PKCS#7 Cryptographic Message Standard specifies the DigestInfo type as ASN.1 structure whose BER encoded value serves as input for the digest-encryption process when creating a SignedData object.

 DigestInfo ::= SEQUENCE {
   digestAlgorithm DigestAlgorithmIdentifier,
   digest Digest }
 

 Digest ::= OCTET STRING
 

The Signed-data content type is used for building digital signatures on some particular content for one or more signers. For each signer, a message digest is computed on the content (and any additional authenticated information) with a signer-specific message-digest algorithm. Resulting message digest and appertaining digest algorithm identifier are collected to form a DigestInfo object, which subsequently is DER encoded for being encrypted with the particular signerīs private key to finally produce the signer-specific digital signature. Signature value and some signer-related information are included into a SignerInfo structure. In that way, for every single signer a specific SignerInfo object is created. All SignerInfos are are collected together with the content for forming a SignedData structure.

The constructors and methods of this class are used by the SignerInfo class for building a DigestInfo to be fed to the digest encryption process, respectively - on the receiverīs side - for creating a DigestInfo on the "re-decrypted" DigestInfo ASN.1 structure when parsing for the inherent digest value.

This class only can be used for creating a DigestInfo for an already computed message digest. This class does not support any mechanisms for computing a message digest.

Example:

 //the message to be hashed:
 byte[] message = "Test data to be digested".getBytes();
 //compute the message digest:
 MessageDigest md = MessageDigest.getInstance("SHA");
 md.update(message);
 byte[] digest = md.digest();
 //create a DigestInfo object and supply the message digest just computed:
 DigestInfo digested_info = new DigestInfo(AlgorithmID.sha, digest);
 

Version:

File Revision 18

See Also:

ContentInfo, SignerInfo, SignedData

Constructor Summary

DigestInfo(AlgorithmID digestAlgorithm, byte[] digest)
Creates a new DigestInfo from a digest algorithm and a digest.

DigestInfo(ASN1Object obj)
Creates a new DigestInfo from an ASN1Object.

Method Summary

void	decode(ASN1Object obj) Decodes the given ASN.1 DigestInfo object for parsing the internal structure.
byte[]	getDigest() Returns the digest value held by this DigestInfo.
AlgorithmID	getDigestAlgorithm() Returns the AlgorithmID of the message-digest algorithm (including any associated parameters) that has been used for calculating the digest on the content and any authenticated information.
ASN1Object	toASN1Object() Returns this DigestInfo as ASN1Object.
byte[]	toByteArray() Returns this DigestInfo as DER encoded byte array.
String	toString() Returns a string giving some information about this DigestInfo object.
String	toString(boolean detailed) Returns a string giving some - if requested - detailed information about this DigestInfo object.

Methods inherited from class java.lang.Object

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

Constructor Detail

DigestInfo

public DigestInfo(AlgorithmID digestAlgorithm,
                  byte[] digest)

Creates a new DigestInfo from a digest algorithm and a digest.

Parameters:

digestAlgorithm - the identifier of the signer-specific digest algorithm (including any associated parameters)

digest - the digest value computed on the content and any authenticated data using the the signer-specific digest algorithm

See Also:

SignerInfo

DigestInfo

public DigestInfo(ASN1Object obj)
           throws CodingException

Creates a new DigestInfo from an ASN1Object.

The ASN1Object supplied to this constructor represents an already exisiting DigestInfo object that may have been created by calling toASN1Object.

Parameters:

obj - obj the PKCS#7 DigestInfo as ASN1Object

Throws:

CodingException - if the object can not be parsed

See Also:

SignerInfo.getDigest(java.security.PublicKey)

Method Detail

decode

public void decode(ASN1Object obj)
            throws CodingException

Decodes the given ASN.1 DigestInfo object for parsing the internal structure.

This method internally is called when creating a PKCS#7 DigestInfo object from an already existing DigestInfo object, supplied as ASN1Object.

Specified by:

decode in interface ASN1Type

Parameters:

obj - the PKCS#7 DigestInfo as ASN1Object

Throws:

CodingException - if the object can not be parsed

toASN1Object

public ASN1Object toASN1Object()

Returns this DigestInfo as ASN1Object.

The ASN1Object returned by this method may be used as parameter value when creating a DigestInfo object using the DigestInfo(ASN1Object obj) constructor.

Specified by:

toASN1Object in interface ASN1Type

Returns:

this DigestInfo as ASN1Object.

toByteArray

public byte[] toByteArray()

Returns this DigestInfo as DER encoded byte array.

This method may be used for DER encoding this DigestInfo object before passing it to the digest encryption process.

Returns:

this DigestInfo as DER encoded byte array

getDigestAlgorithm

public AlgorithmID getDigestAlgorithm()

Returns the AlgorithmID of the message-digest algorithm (including any associated parameters) that has been used for calculating the digest on the content and any authenticated information.

Returns:

the AlgorithmID of the message-digest algorithm

getDigest

public byte[] getDigest()

Returns the digest value held by this DigestInfo.

Returns:

the digest value in a byte array

toString

public String toString()

Returns a string giving some information about this DigestInfo object.

Overrides:

toString in class Object

Returns:

the string representation

toString

public String toString(boolean detailed)

Returns a string giving some - if requested - detailed information about this DigestInfo object.

Parameters:

detailed - - whether or not to give detailed information

Returns:

the string representation