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unzip-6.0/proginfo/extrafld.txt  view on Meta::CPAN

          This field contains the information about which certificate in
          the PKCS#7 store was used to sign a particular file.  It also
          contains the signature data.  This field can appear multiple
          times, but can only appear once per certificate.

          Note: all fields stored in Intel low-byte/high-byte order.

          Value         Size        Description
          -----         ----        -----------
  (CID)   0x0015        2 bytes     Tag for this "extra" block type
          CSize         2 bytes     Size of Method
          Method        (variable)

          Method
          Value         Size        Description
          -----         ----        -----------
          Version       2 bytes     Version number, for now 0x0001
          AlgID         2 bytes     Algorithm ID used for signing
          IDSize        2 bytes     Size of Certificate ID data
          CertID        (variable)  Certificate ID data
          SigSize       2 bytes     Size of Signature data
          Sig           (variable)  Signature data

          CertID
          Value         Size        Description
          -----         ----        -----------
          Size1         4 bytes     Size of CertID, should be (IDSize - 4)
          Size1         4 bytes     A bug in version one causes this value
                                    to appear twice.
          IssSize       4 bytes     Issuer data size
          Issuer        (variable)  Issuer data
          SerSize       4 bytes     Serial Number size
          Serial        (variable)  Serial Number data

          The Issuer and IssSize members are suitable for creating a
          CRYPT_DATA_BLOB to be the Issuer member of a CERT_INFO
          struct. The Serial and SerSize members would be the
          SerialNumber member of the same CERT_INFO struct.  This
          struct would be used to find the certificate in the store
          the file was signed with.  Those structures are from the MS
          CryptoAPI.

          Sig and SigSize are the actual signature data and size
          generated by signing the file with the MS CryptoAPI using a
          hash created with the given AlgID.


         -X.509 Certificate ID and Signature for central directory (0x0016):
          =================================================================

          This field contains the information about which certificate in
          the PKCS#7 store was used to sign the central directory structure.
          When the Central Directory Encryption feature is enabled for a
          ZIP file, this record will appear in the Archive Extra Data Record,
          otherwise it will appear in the first central directory record,
          along with the store.  The data structure is the
          same as the CID, except that SigSize will be 0, and there
          will be no Sig member.

          This field is also kept after the last central directory
          record, as the signature data (ID 0x05054b50, it looks like
          a central directory record of a different type).  This
          second copy of the data is the Signature Data member of the
          record, and will have a SigSize that is non-zero, and will
          have Sig data.

          Note: all fields stored in Intel low-byte/high-byte order.

          Value     Size     Description
          -----     ----     -----------
  (CDID)  0x0016    2 bytes  Tag for this "extra" block type
          TSize     2 bytes  Size of data that follows
          TData     TSize    Data


         -Strong Encryption Header (0x0017):
          =================================

          Value     Size     Description
          -----     ----     -----------
          0x0017    2 bytes  Tag for this "extra" block type
          TSize     2 bytes  Size of data that follows
          Format    2 bytes  Format definition for this record
          AlgID     2 bytes  Encryption algorithm identifier
          Bitlen    2 bytes  Bit length of encryption key
          Flags     2 bytes  Processing flags
          CertData  TSize-8  Certificate decryption extra field data
                             (refer to the explanation for CertData
                              in the section describing the
                              Certificate Processing Method under
                              the Strong Encryption Specification)


         -Record Management Controls (0x0018):
          ===================================

          Value     Size     Description
          -----     ----     -----------
(Rec-CTL) 0x0018    2 bytes  Tag for this "extra" block type
          CSize     2 bytes  Size of total extra block data
          Tag1      2 bytes  Record control attribute 1
          Size1     2 bytes  Size of attribute 1, in bytes
          Data1     Size1    Attribute 1 data
            .
            .
            .
          TagN      2 bytes  Record control attribute N
          SizeN     2 bytes  Size of attribute N, in bytes
          DataN     SizeN    Attribute N data


         -PKCS#7 Encryption Recipient Certificate List (0x0019):
          =====================================================

          This field contains information about each of the certificates
          used in encryption processing and it can be used to identify who is
          allowed to decrypt encrypted files.  This field should only appear
          in the archive extra data record. This field is not required and
          serves only to aide archive modifications by preserving public
          encryption key data. Individual security requirements may dictate
          that this data be omitted to deter information exposure.