iaik.pkcs.pkcs7

Class DigestInfo

java.lang.Object

iaik.pkcs.pkcs7.DigestInfo

All Implemented Interfaces:

ASN1Type

public class DigestInfo
extends java.lang.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 signer's 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 receiver's 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 20

See Also:

ContentInfo, SignerInfo, SignedData

Constructor Summary

Constructors

Constructor and Description
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.
DigestInfo(byte[] array) Creates a new DigestInfo from its DER encoding.

Method Summary

Modifier and Type	Method and Description
boolean	checkDigestAlgorithm(AlgorithmID digestAlgorithm) Compares the digest algorithm of this DigestInfo with the given digest algorithm.
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.
java.lang.String	toString() Returns a string giving some information about this DigestInfo object.
java.lang.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(byte[] array)
           throws CodingException

Creates a new DigestInfo from its DER encoding.

Parameters:

array - the DER encoded DigestInfo

Throws:

CodingException - if an error occurs when decoding the DigestInfo

DigestInfo

public DigestInfo(ASN1Object obj)
           throws CodingException

Creates a new DigestInfo from an ASN1Object.

The ASN1Object supplied to this constructor represents an already existing 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

checkDigestAlgorithm

public boolean checkDigestAlgorithm(AlgorithmID digestAlgorithm)

Compares the digest algorithm of this DigestInfo with the given digest algorithm. A digest algorithm check shall be performed during signature verification.

Parameters:

digestAlgorithm - the digest algorithm to be compared with the digest algorithm of this DigestInfo

Returns:

true if the two algorithm identifier are equal ( NULL as parameter is treated as being equal to a missing parameter field), false if they are not equal

getDigest

public byte[] getDigest()

Returns the digest value held by this DigestInfo.

Returns:

the digest value in a byte array

toString

public java.lang.String toString()

Returns a string giving some information about this DigestInfo object.

Overrides:

toString in class java.lang.Object

Returns:

the string representation

toString

public java.lang.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