NAME

dcmsign - Sign and Verify DICOM Files

SYNOPSIS

dcmsign [options] dcmfile-in [dcmfile-out]

DESCRIPTION

The dcmsign utility reads a DICOM file (dcmfile-in), performs a digital signature operation and, if any modification has taken place, writes the DICOM object to an output file (dcmfile-out).

Five digital signature operations are supported:

verification of all signatures in the DICOM file
creation of a new digital signature located in the main dataset,
creation of a new digital signature in an item of a sequence embedded within the dataset,
removal of a single digital signature from the DICOM file, and
removal of all digital signatures from the DICOM file.

PARAMETERS

dcmfile-in   DICOM input filename to be processed
dcmfile-out  DICOM output filename

OPTIONS

general options

  -h    --help
          print this help text and exit
        --version
          print version information and exit
        --arguments
          print expanded command line arguments
  -q    --quiet
          quiet mode, print no warnings and errors
  -v    --verbose
          verbose mode, print processing details
  -d    --debug
          debug mode, print debug information
  -ll   --log-level  [l]evel: string constant
          (fatal, error, warn, info, debug, trace)
          use level l for the logger
  -lc   --log-config  [f]ilename: string
          use config file f for the logger

input options

input file format:
  +f    --read-file
          read file format or data set (default)
  +fo   --read-file-only
          read file format only
  -f    --read-dataset
          read data set without file meta information
input transfer syntax:
  -t=   --read-xfer-auto
          use TS recognition (default)
  -td   --read-xfer-detect
          ignore TS specified in the file meta header
  -te   --read-xfer-little
          read with explicit VR little endian TS
  -tb   --read-xfer-big
          read with explicit VR big endian TS
  -ti   --read-xfer-implicit
          read with implicit VR little endian TS
handling of defined length UN elements:
  -uc   --retain-un
          retain elements as UN (default)
  +uc   --convert-un
          convert to real VR if known

signature commands

        --verify
          verify all signatures (default)
  +s    --sign  [p]rivate key file, [c]ertificate file: string
          create signature in main object
  +si   --sign-item  [k]eyfile, [c]ertfile, [i]tem location: string
          create signature in sequence item
  +t    --insert-timestamp  ts[q]file, ts[r]file [u]idfile: string
          insert certified timestamp from ts response r
          from timestamp query q at signature UID u
  +r    --remove  [s]ignature UID: string
          remove signature
  +ra   --remove-all
          remove all signatures from data set

general signature options

key and certificate file format:
  -pem  --pem-keys
          read keys/certificates as PEM file (default)
  -der  --der-keys
          read keys/certificates as DER file
signature format:
  -fn   --format-new
          use correct DICOM signature format (default)
  -fo   --format-old
          use old (pre-3.5.4) DCMTK signature format, non-conformant
          if signature includes compressed pixel data. This option should
          only be used to verify signatures in the old format.

signature verification options (only with –verify)

signature verification:
  +rv   --verify-if-present
          verify signatures if present, pass otherwise
          (default)
  +rg   --require-sig
          fail if no signature at all is present
  +rc   --require-creator
          fail if no creator RSA signature is present
  +ru   --require-auth
          fail if no auth RSA signature is present
  +rs   --require-sr
          fail if no SR RSA signature is present
timestamp verification:
  +tv   --verify-ts
          verify certified timestamp if present (default)
  -tv   --ignore-ts
          ignore certified timestamps
  +tr   --require-ts
          fail if no certified timestamp is present
certification authority:
  +cf   --add-cert-file
          [f]ilename: string
          add trusted certificate file to cert store
  +uf   --add-ucert-file
          [f]ilename: string
          add untrusted intermediate certificate file
  +cd   --add-cert-dir
          [d]irectory: string
          add certificates in d to cert store
  +cr   --add-crl-file
          [f]ilename: string
          add certificate revocation list file
          (implies --enable-crl-vfy)
  +cl   --enable-crl-vfy
          enable certificate revocation list verification.fi

signature creation options (only with –sign or –sign-item)

private key password:
  +ps   --std-passwd
          prompt user to type password on stdin (default)
  +pw   --use-passwd  [p]assword: string
          use specified password
  -pw   --null-passwd
          use empty string as password
digital signature profile:
  -pf   --profile-none
          don't enforce any signature profile (default)
  +pb   --profile-base
          enforce base RSA signature profile
  +pc   --profile-creator
          enforce creator RSA signature profile
  +pa   --profile-auth
          enforce authorization signature profile
  +pr   --profile-sr
          enforce SR RSA signature profile
  +pv   --profile-srv
          enforce SR RSA signature profile (verification)
MAC algorithm:
  +mr   --mac-ripemd160
          use RIPEMD 160 (default)
  +ms   --mac-sha1
          use SHA-1
  +mm   --mac-md5
          use MD 5
  +m2   --mac-sha256
          use SHA-256
  +m3   --mac-sha384
          use SHA-384
  +m5   --mac-sha512
          use SHA-512
signature purpose:
  +lp   --list-purposes
          show list of signature purpose codes and exit
  -sp   --no-sig-purpose
          do not add signature purpose (default)
  +sp   --sig-purpose
          [p]urpose code: integer (1..18)
          add digital signature purpose code p
tag selection:
  -t    --tag
          [t]ag: "gggg,eeee" or dictionary name
          sign only specified tag
          (this option can be specified multiple times)
  -tf   --tag-file  [f]ilename: string
          read list of tags from text file.fi

timestamp creation options (only with –sign or –sign-item)

timestamp creation:
  -ts   --timestamp-off
          do not create timestamp (default)
  +ts   --timestamp-file  [t]sq-filename, [u]id-filename: string
          create timestamp query file t and uid file u
timestamp MAC algorithm (only with --timestamp-file):
  +tm2  --ts-mac-sha256
          use SHA-256 (default)
  +tm3  --ts-mac-sha384
          use SHA-384
  +tm5  --ts-mac-sha512
          use SHA-512
  +tmr  --ts-mac-ripemd160
          use RIPEMD 160
  +tms  --ts-mac-sha1
          use SHA-1 (not recommended)
  +tmm  --ts-mac-md5
          use MD5 (not recommended)
timestamp query nonce options (only with --timestamp-file):
  +tn   --ts-use-nonce
          include random nonce (default)
  -tn   --ts-no-nonce
          do not include nonce
timestamp certificate inclusion options (only with --timestamp-file):
  +tc   --ts-request-cert
          request TSA certificate in timestamp (default)
  -tc   --ts-no-cert
          do not request TSA certificate in timestamp
timestamp policy options (only with --timestamp-file):
  -tp   --ts-no-policy
          do not specify ts policy (default)
  +tp   --ts-policy  [p]olicy-OID: string
          request timestamp policy p

output options

output transfer syntax:
  +t=   --write-xfer-same
          write with same TS as input (default)
  +te   --write-xfer-little
          write with explicit VR little endian TS
  +tb   --write-xfer-big
          write with explicit VR big endian TS
  +ti   --write-xfer-implicit
          write with implicit VR little endian TS
length encoding in sequences and items:
  +e    --length-explicit
          write with explicit lengths (default)
  -e    --length-undefined
          write with undefined lengths
other output options:
  +d    --dump  [f]ilename: string
          dump byte stream fed into the MAC codec to file
          (only with --sign or --sign-item)

NOTES

Files and Parameters

The dcmsign utility reads and writes a number of files and file formats which are described in this section.

Public Key Certificates are expected in X.509v3 format, either with PEM or DER encoding. The dcmsign utility currently supports RSA and DSA public keys, although only RSA keys are defines in the Security Profiles of the DICOM standard.

Private Keys are expected in PEM or DER encoding. PEM is recommended (and default) because this allows one to keep private keys in encrypted form. Command line options control the behavior of dcmsign when an encrypted PEM key is opened (see above). In general it is not recommended to specify the encryption password in the command line because the command line may be visible to other processes in the system, e.g. 'ps -ef'.

By default, dcmsign will create a signature covering all data elements in the dataset or item. This default can be overridden by explicitly specifying a list of data elements (attribute tags). This list can either be read from a file or specified on the command line or both (in this case the attribute tags are combined).

On the command line, attribute tags are specified as

--tag "gggg,eeee"  where gggg and eeee are the hexadecimal group
                   and element numbers
--tag "Name"       where 'Name' is a symbolic attribute name from
                   the DICOM dictionary (see below).

When attribute tags are read from file with the --tag-file option, a plain text file is expected. Tags within the file are either symbolic names from the data dictionary or have the format (gggg,eeee) (with braces). Tags are separated by one or more whitespace characters.

The currently selected digital signature profile may specify additional attribute tags required to be included in the signature, which will be silently added.

The --sign-item operation requires a location string that describes in which sequence item a signature is to be created. The location string has the following format:

SequenceName[index].SequenceName[index].SequenceName[index](...)

where SequenceName is either a symbolic attribute name from the data dictionary or a numeric tag in the format (gggg,eeee) and index is an unsigned decimal integer for the item number, starting with zero for the first item in a sequence. As an example, the following location string

ReferencedSeriesSequence[0].ReferencedImageSequence[1]

would cause a digital signature to be created in the second item of the ReferencedImageSequence (0008,1140) which is located in the first item of the ReferencedSeriesSequence (0008,1115) which is located in the main DICOM dataset.

Certified Timestamps

Starting with release 3.6.6, dcmsign offers support for certified timestamps according to RFC 3161. For now, the tool does not implement any of the network protocols defined in RFC 3161 for communicating with a timestamp authority (TSA), but it can write a timestamp query (TSQ) during signature creation, and the new command --insert-timestamp will read a timestamp response (TSR) from file and add it to the DICOM digital signature. Since a DICOM file can contain multiple signatures, a 'UID file' (which contains the Digital Signature UID) is used to identify the signature to which the TSR should be added. The dcmsign tool will also perform various consistency checks before storing the timestamp.

During signature verification, the presence of a certified timestamp will be detected and the timestamp will also be verified unless option --ignore-ts was used. Signature verification and timestamp verification use a common certificate store to check the certificates of the DICOM signature and the timestamp. This store can be populated with the options --add-cert-file and --add-cert-dir, which both add trusted CA certificates, --add-ucert-file, which adds an untrusted intermediate CA certificate, and --add-crl-file, which adds a certificate revocation list.

Hashed Certificate Directories

Instead of adding CA certificates and certificate revocation lists (CRLs) manually using --add-cert-file and --add-crl-file, the user can set-up a directory where dcmsign will look-up and load certificates and CRLs from as needed, using --add-cert-dir.

Th directory should contain one certificate or CRL per file in PEM format, with a filename of the form hash.N for a certificate, or hash.rN for a CRL. The hash is the value returned by

openssl x509 -hash -noout -in <filename.pem> (for a certificate) openssl crl -hash -noout -in <filename.pem> (for a CRL)

The .N or .rN suffix is a sequence number that starts at zero, and is incremented consecutively for each certificate or CRL with the same hash value. Gaps in the sequence numbers are not supported, it is assumed that there are no more objects with the same hash beyond the first missing number in the sequence.

CRLs will only be verified when option --enable-crl-vfy is specified. In this case, dcmsign will expect a CRL to be present for each CA and will fail signature verification if no CRL can be found for the CA that issued the signer certificate.

LOGGING

The level of logging output of the various command line tools and underlying libraries can be specified by the user. By default, only errors and warnings are written to the standard error stream. Using option --verbose also informational messages like processing details are reported. Option --debug can be used to get more details on the internal activity, e.g. for debugging purposes. Other logging levels can be selected using option --log-level. In --quiet mode only fatal errors are reported. In such very severe error events, the application will usually terminate. For more details on the different logging levels, see documentation of module 'oflog'.

In case the logging output should be written to file (optionally with logfile rotation), to syslog (Unix) or the event log (Windows) option --log-config can be used. This configuration file also allows for directing only certain messages to a particular output stream and for filtering certain messages based on the module or application where they are generated. An example configuration file is provided in <etcdir>/logger.cfg.

COMMAND LINE

All command line tools use the following notation for parameters: square brackets enclose optional values (0-1), three trailing dots indicate that multiple values are allowed (1-n), a combination of both means 0 to n values.

Command line options are distinguished from parameters by a leading '+' or '-' sign, respectively. Usually, order and position of command line options are arbitrary (i.e. they can appear anywhere). However, if options are mutually exclusive the rightmost appearance is used. This behavior conforms to the standard evaluation rules of common Unix shells.

In addition, one or more command files can be specified using an '@' sign as a prefix to the filename (e.g. @command.txt). Such a command argument is replaced by the content of the corresponding text file (multiple whitespaces are treated as a single separator unless they appear between two quotation marks) prior to any further evaluation. Please note that a command file cannot contain another command file. This simple but effective approach allows one to summarize common combinations of options/parameters and avoids longish and confusing command lines (an example is provided in file <datadir>/dumppat.txt).

EXIT CODES

The dcmsign utility uses the following exit codes when terminating. This enables the user to check for the reason why the application terminated.

general

EXITCODE_NO_ERROR                         0
EXITCODE_COMMANDLINE_SYNTAX_ERROR         1
EXITCODE_NOOPENSSL                        5

input file errors

EXITCODE_CANNOT_READ_INPUT_FILE          20
EXITCODE_NO_INPUT_FILES                  21
EXITCODE_CANNOT_READ_TAG_FILE            30
EXITCODE_CANNOT_READ_TSQ_FILE            31
EXITCODE_CANNOT_READ_TSR_FILE            32
EXITCODE_CANNOT_READ_UID_FILE            33

output file errors

EXITCODE_CANNOT_WRITE_OUTPUT_FILE        40
EXITCODE_CANNOT_WRITE_SUPPORT_FILE       46

processing errors

EXITCODE_CANNOT_ACCESS_SIGNATURE         80
EXITCODE_CANNOT_ACCESS_TS                81
EXITCODE_CANNOT_INSERT_TS                82
EXITCODE_SIGNATURE_REMOVAL_FAILED        83
EXITCODE_SIGNATURE_UID_NOT_FOUND         84
EXITCODE_SIGNATURE_CREATION_FAILED       85
EXITCODE_SYNTAX_ERROR_IN_TAG_FILE        86
EXITCODE_TS_CONSISTENCY_CHECK_FAILED     87

application specific errors

EXITCODE_NO_SIGNATURES_PRESENT           100
EXITCODE_SIGNATURE_VERIFICATION_FAILED   101
EXITCODE_SIGNATURE_VERIFICATION_POLICY   102

ENVIRONMENT

The dcmsign utility will attempt to load DICOM data dictionaries specified in the DCMDICTPATH environment variable. By default, i.e. if the DCMDICTPATH environment variable is not set, the file <datadir>/dicom.dic will be loaded unless the dictionary is built into the application (default for Windows).

The default behavior should be preferred and the DCMDICTPATH environment variable only used when alternative data dictionaries are required. The DCMDICTPATH environment variable has the same format as the Unix shell PATH variable in that a colon (':') separates entries. On Windows systems, a semicolon (';') is used as a separator. The data dictionary code will attempt to load each file specified in the DCMDICTPATH environment variable. It is an error if no data dictionary can be loaded.