public class DigestedData extends DigestedDataStream implements Content
DigestedData type.
Each CMS content type is associated with a specific object identifier, derived from:
pkcs-7 OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) US(840) rsadsi(113549)
pkcs(1) 7 }
The object identifier for the DigestedData content type is
defined as:
digestedData OBJECT IDENTIFIER ::= { pkcs-7 5 }
which corresponds to the OID string "1.2.840.1.113549.1.7.5".
The Cryptographic Message Syntax
(CMS, RFC 2630) specifies the DigestedData
content type for providing a syntax for building message digests. The
digested-data content type consists of content of any type and a message
digest of the content (Version 1.5):
DigestedData ::= SEQUENCE {
version Version,
digestAlgorithm DigestAlgorithmIdentifier,
encapContentInfo EncapsulatedContentInfo,
digest Digest }
Digest ::= OCTET STRING
The digestAlgorithm field specifies the digest algorithm to be
used for computing the message digest of the content given in the
contentInfo field. The result of the digest calculation is stored
in the digest field.
Verifying a received message digest is done by comparing it with an
independently computed message digest.
When creating a DigestedData object for the content to be
digested by using the DigestedData(byte[] content, AlgorithmID digestAlgorithm, int mode)
constructor, additionally the transimission mode has to be specified. If the mode is
set to DigestedData.IMPLICIT the raw data will be included in the
DigestedData message to be transmitted, but it will be not included
if the mode is set to DigestedData.EXPLICIT.
However, in both cases the raw data has to be supplied when creating the
DigestedData object, because it is needed for the digest
computation:
byte[] content = ...; // the raw data to be digested AlgorithmID digestAlg = ...; DigestedData digested_data = new DigestedData(content, digestAlg, DigestedData.IMPLICIT);respectively
DigestedData digested_data = new DigestedData(content, digestAlg, DigestedData.EXPLICIT);In contrast to the stream-variant of the CMS DigestedData type (implemented by the
DigestedDataStream class),
where explicit and implicit mode have to be handled in different way when creating
a DigestedData object, they have the same proceeding for this non-stream-supporting
DigestedData class.
In this way, after having created a DigestedData object the only remaining
task is to prepare the DigestedData object for transmission by transforming it into an
ASN1Object or immediately DER encoding it. The former is done by calling the
toASN1Object method, the latter by using the getEncoded method:
ASN1Object obj = digested_data.toASN1Object();respectively
byte[] encoding = digested_data.getEncoded();You alternatively may use a proper
writeTo method of the parent
DigestedDataStream class for immediately
encoding this DigestedData object to an output stream. When using writeTo in
implicit mode, you additionally have the possibility of specifying a particular blockSize
for forcing an indefinite constructed encoding of the inherent raw data bytes, instead of
of the default definite primitive encoding, e.g:
0x24 0x80
0x04 0x02 0x01 0xAB
0x04 0x02 0x23 0x7F
0x04 0x01 0xCA
0x00 0x00
instead of:
0x04 0x05 0x01 0xAB 0x23 0x7F 0xCAfor encoding the five data bytes
0x01 0xAB 0x23 0x7F 0xCA. The indefinte
constrcuted encoding scheme may be preferable when intending to be compatible to the
encoding practice of some particular application (for instance some versions of
Netscape Navigator).
Unlike the procedure of newly creating a DigestedData object to be transmitted, even when
using this non-stream implementation of the DigestedData content type, it
has to be distinguished between IMPLICIT and EXPLICIT mode when parsing a received
DigestedData message. When operating in IMPLICIT mode, the raw data is included in
the received DigestedData object, and so the parsing immediately may be
performed when creating a DigestedData object from the
DigestedData ASN1Object by calling the DigestedData(ASN1Object obj) constructor. On the other side, when the raw data has
been transmitted outside the DigestedData message (EXPLICIT mode), the
DigestedData(byte[] content,
AlgorithmID digestAlgorithm) constructor has be to used for initializing the new
DigestedData object with raw data and hash algorithm to be used for digest computation;
and the decoding has to be performed explicitly by calling the decode method. The initialization is necessary for computing the digest on the raw
data for the supplied digest algorithm. Later, during digest verification this
digest value has to be compared against the hash value sent within the digest
field.
All further steps are the same for implicit and explicit mode, and so the proceeding
necessary for parsing a received DigestedData message and verifying the digest
may be summarized as follows:
ASN1Object obj = DerCoder.decode(received_message);
DigestedData(ASN1Object obj)
constructor for creating a DigestedData object and implicitly parsing the
the supplied ASN.1 structure:
DigestedData digestedData = new DigestedData(obj);
On the other hand, if the ASN1Object resulting from step 1 above represents an
explicit DigestedData object, use the
DigestedData(byte[] content, AlgorithmID digestAlgorithm)
constructor for initializing a new DigestedData object with raw data and
digest algorithm for hash computation, and subsequently explicitly perform
the decoding by means of the decode
method (assuming that the SHA-1 hash algorithm is used):
AlgorithmID algIDs = AlgorithmID.sha1;
DigestedData digestedData = new DigestedData(raw_data, algID);
digestedData.decode(obj);
if (digestedData.verify()) {
System.out.println("Hash ok!");
else
System.out.println("Message corrupted!");
byte[] data = digestedData.getContent();
Use the stream supporting DigestedDataStream parent class for handling structures with large
amounts of data.
blockSize_, contentType_, digestAlgorithm_, encapContentInfo_, EXPLICIT, IMPLICIT, inputStream_, mode_, version_| Modifier | Constructor and Description |
|---|---|
protected |
DigestedData()
Default constructor for dynamic object creation in ContentInfo.
|
|
DigestedData(ASN1Object obj)
Creates a CMS
DigestedData from an ASN1Object. |
|
DigestedData(byte[] content,
AlgorithmID digestAlgorithm)
Creates a new DigestedData from a byte array holding the content that
has been transmitted by other means, and the hash algorithm to be used
for digesting.
|
|
DigestedData(byte[] content,
AlgorithmID digestAlgorithm,
int mode)
Creates a new
DigestedData object from given content and
and digest algorithm. |
|
DigestedData(java.io.InputStream is)
Creates a CMS DigestedData from an InputStream.
|
|
DigestedData(ObjectID contentType,
AlgorithmID digestAlgorithm,
byte[] digest)
Creates a new
DigestedData object without content. |
|
DigestedData(ObjectID contentType,
byte[] content,
AlgorithmID digestAlgorithm,
int mode)
Creates a new
DigestedData object from given content and
and digest algorithm. |
| Modifier and Type | Method and Description |
|---|---|
void |
decode(ASN1Object obj)
Decodes the given DigestedData ASN1 object.
|
void |
decode(java.io.InputStream is)
Reads and decodes the encoded DigestedData from an input stream.
|
byte[] |
getContent()
Returns the content.
|
byte[] |
getEncoded()
Returns the encoding of this DigestedData in a byte array.
|
java.io.InputStream |
getInputStream()
Returns an InputStream from which the contents of this object can be read.
|
protected void |
setupMessageDigest(AlgorithmID digestAlgorithm,
boolean parse)
Calculates the digest.
|
protected ASN1Object |
toASN1Object(int blockSize)
Returns this
DigestedData as ASN1Object. |
java.lang.String |
toString(boolean detailed)
Returns a string giving some - if requested - detailed information
about this
DigestedData object. |
encodeCalled, getBlockSize, getContentType, getDigest, getDigestAlgorithm, getEncapsulatedContentType, getVersion, notifyEOF, setBlockSize, setDigest, toASN1Object, toString, verify, writeTo, writeToclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitgetBlockSize, getContentType, setBlockSize, toASN1Objectprotected DigestedData()
public DigestedData(byte[] content,
AlgorithmID digestAlgorithm,
int mode)
throws CMSException
DigestedData object from given content and
and digest algorithm.
The data to be digested is supplied as byte array. The mode parameter
specifies whether to include the data (mode = DigestedDataStream.IMPLICIT) or
not include it (mode = DigestedDataStream.EXPLICIT). The content type of the
inherent EncapsulatedContentInfo automatically is set to CMS Data.content - the data to be digested supplied from a byte arraydigestAlgorithm - the message-digest algorithm to be used for creating the digestmode - either Digested.IMPLICIT for including the data, or
DigestedData.EXPLICIT for not including itCMSException - if the supplied paramteres to not satisfy the requirements ot there is no
implementation for the requested hash algorithmpublic DigestedData(ObjectID contentType, byte[] content, AlgorithmID digestAlgorithm, int mode) throws CMSException
DigestedData object from given content and
and digest algorithm.
The data to be digested is supplied as byte array. The mode parameter
specifies whether to include the data (mode = DigestedDataStream.IMPLICIT) or
not include it (mode = DigestedDataStream.EXPLICIT).contentTpe - the content type of the data to be digestedcontent - the data to be digested supplied from a byte arraydigestAlgorithm - the message-digest algorithm to be used for creating the digestmode - either Digested.IMPLICIT for including the data, or
DigestedData.EXPLICIT for not including itCMSException - if the supplied paramteres to not satisfy the requirements ot there is no
implementation for the requested hash algorithmpublic DigestedData(ObjectID contentType, AlgorithmID digestAlgorithm, byte[] digest)
DigestedData object without content.
For instance:
byte[] message = "Test data to be digested".getBytes();
MessageDigest md = MessageDigest.getInstance("SHA", "IAIK");
md.update(message);
byte[] digest = md.digest();
DigestedData digested_data = new DigestedData(ObjectID.cms_data, AlgorithmID.sha1, digest);
The content must be supplied by other means.
contentType - the content type of the digested datadigestAlgorithm - the message-digest algorithm (and any associated parameters)
used for creating the digestdigest - the result of the message-digesting processpublic DigestedData(ASN1Object obj) throws CMSParsingException
DigestedData from an ASN1Object.
Do not use this constructor for supplying content and
hashed content value.
This constructor may be used by the recipient for parsing an
already exisiting DigestedData object, supplied as ASN1Object
that may have been created by calling
toASN1Object.
Use the DigestedData(byte[] content, AlgorithmID digestAlgorithm, int mode)
constructor for supplying content and hashed content value
when creating a DigestedData object.
obj - the CMS DigestedData as ASN1ObjectCMSParsingException - if the object can not be parsedpublic DigestedData(java.io.InputStream is)
throws java.io.IOException,
CMSParsingException
is - the InputStream holding the encoded CMS DigestedData objectjava.io.IOException - if an error occurs when reasding from the streamCMSParsingException - if the object can not be parsedpublic DigestedData(byte[] content,
AlgorithmID digestAlgorithm)
throws java.security.NoSuchAlgorithmException
Do not use this constructor for supplying the content value
to be digested. This constructor may be used by the recipient for initializing
the digest computation for an already existing explicit DigestedData message
where the raw data is not included. In contrast to
the equivalent constructor of the parent DigestedDataStream class, this constructor not only initializes
the digest computation, but also already computes the digest for the given
digest algorithm. Later, during digest verification these digest value have
to be compared against the hash value sent in the digest field.
For subsequently performing the decoding
of the received explicit DigestedData object, use the decode
method:
//initialize - and perform - digest computaion: DigestedData digestedData = new DigestedData(raw_data, hashAlgorithm); //parse the received DigestedData ASN1Object ASN1Object obj = DerCoder.decode(encodedDigestesData); digestedData.decode(obj);
A sender shall use the DigestedData(byte[] content, AlgorithmID digestAlgorithm, int mode)
constructor for supplying the content value to be digested when creating a
DigestedData object.
For parsing an implicit DigestedData message, use the DigestedData(ASN1Object obj) constructor.
content - the content transmitted by other meansdigestAlgorithm - the hash algorithm used for digesting the
content datajava.security.NoSuchAlgorithmException - if the supplied hash algorithm is not supportedprotected void setupMessageDigest(AlgorithmID digestAlgorithm, boolean parse) throws java.security.NoSuchAlgorithmException
digestAlgorithm - the digest algorithm to be usedjava.security.NoSuchAlgorithmException - if the digestAlgorithm is not supportedpublic void decode(ASN1Object obj) throws CMSParsingException
decode in interface Contentobj - the ASN1Object representing an already exisiting DigestedData objectCMSParsingException - if an error occurs when parsing the given ASN1Objectpublic void decode(java.io.InputStream is)
throws java.io.IOException,
CMSParsingException
decode in interface ContentStreamdecode in class DigestedDataStreamis - the InputStream supplying a DER encoded CMS DigestedData objectjava.io.IOException - if an I/O error occurs during reading from the InputStreamCMSParsingException - if an error occurs while parsing the objectpublic java.io.InputStream getInputStream()
This method only overrides the corresponding getInputStream method
of the parent DigestedDataStream
class for returning the content of this DigestedData object.
There should be no real necessity for using this method since the raw data
bytes immediately can be obtained by the getContent method.
However, in contrast to the equivalent getInputStream method of the
parent DigesetdDataStream class, this method may be called arbitrarly often;
it only returns a ByteArrayInputStream that is initialized with the raw content bytes.
getInputStream in class DigestedDataStreamDigestedData objectpublic byte[] getContent()
public byte[] getEncoded()
throws CMSException
CMSException - if an error occurs durin gthe encoding procedureprotected ASN1Object toASN1Object(int blockSize) throws CMSException
DigestedData as ASN1Object.
The ASN1Object returned by this method may be used as parameter value when
creating a DigestedData object using the
DigestedData(ASN1Object obj)
constructor.
toASN1Object in class DigestedDataStreamthe - blockSize to be used for block oriented encodingDigestedData as ASN1Object.CMSException - if the ASN1Object could not be createdpublic java.lang.String toString(boolean detailed)
DigestedData object.toString in interface ContentStreamtoString in class DigestedDataStreamdetailed - - whether or not to give detailed information