|1.||The TSA client computes a one-way hash value for a data file and sends the hash to the TSA.|
|2.||The TSA attaches the current date and time to the received hash value, signs them and sends the time stamp token back to the client. By creating this token the TSA certifies the existence of the original data file at the time of response generation.|
|3.||The TSA client receives the time stamp token and verifies the signature on it. It also checks if the token contains the same hash value that it had sent to the TSA.|
There is no support for sending the requests/responses automatically over HTTP or TCP yet as suggested in RFC 3161. The users must send the requests either by ftp or e-mail.
The -query switch can be used for creating and printing a time stamp request with the following options:
-rand file:file... The files containing random data for seeding the random number generator. Multiple files can be specified, the separator is ; for MS-Windows, , for VMS and : for all other platforms. (Optional) -config configfile The configuration file to use, this option overrides the OPENSSL_CONF environment variable. Only the OID section of the config file is used with the -query command. (Optional) -data file_to_hash The data file for which the time stamp request needs to be created. stdin is the default if neither the -data nor the -digest parameter is specified. (Optional) -digest digest_bytes It is possible to specify the message imprint explicitly without the data file. The imprint must be specified in a hexadecimal format, two characters per byte, the bytes optionally separated by colons (e.g. 1A:F6:01:... or 1AF601...). The number of bytes must match the message digest algorithm in use. (Optional) -md2|-md4|-md5|-sha|-sha1|-mdc2|-ripemd160|... The message digest to apply to the data file, it supports all the message digest algorithms that are supported by the openssl dgst command. The default is SHA-1. (Optional) -policy object_id The policy that the client expects the TSA to use for creating the time stamp token. Either the dotted OID notation or OID names defined in the config file can be used. If no policy is requested the TSA will use its own default policy. (Optional) -no_nonce No nonce is specified in the request if this option is given. Otherwise a 64 bit long pseudo-random none is included in the request. It is recommended to use nonce to protect against replay-attacks. (Optional) -cert The TSA is expected to include its signing certificate in the response. (Optional) -in request.tsq This option specifies a previously created time stamp request in DER format that will be printed into the output file. Useful when you need to examine the content of a request in human-readable
-out request.tsq Name of the output file to which the request will be written. Default is stdout. (Optional) -text If this option is specified the output is human-readable text format instead of DER. (Optional)
A time stamp response (TimeStampResp) consists of a response status and the time stamp token itself (ContentInfo), if the token generation was successful. The -reply command is for creating a time stamp response or time stamp token based on a request and printing the response/token in human-readable format. If -token_out is not specified the output is always a time stamp response (TimeStampResp), otherwise it is a time stamp token (ContentInfo).
-config configfile The configuration file to use, this option overrides the OPENSSL_CONF environment variable. See CONFIGURATION FILE OPTIONS for configurable variables. (Optional) -section tsa_section The name of the config file section conatining the settings for the response generation. If not specified the default TSA section is used, see CONFIGURATION FILE OPTIONS for details. (Optional) -queryfile request.tsq The name of the file containing a DER encoded time stamp request. (Optional) -passin password_src Specifies the password source for the private key of the TSA. See PASS PHRASE ARGUMENTS in openssl(1). (Optional) -signer tsa_cert.pem The signer certificate of the TSA in PEM format. The TSA signing certificate must have exactly one extended key usage assigned to it: timeStamping. The extended key usage must also be critical, otherwise the certificate is going to be refused. Overrides the signer_cert variable of the config file. (Optional) -inkey private.pem The signer private key of the TSA in PEM format. Overrides the signer_key config file option. (Optional) -chain certs_file.pem The collection of certificates in PEM format that will all be included in the response in addition to the signer certificate if the -cert option was used for the request. This file is supposed to contain the certificate chain for the signer certificate from its issuer upwards. The -reply command does not build a certificate chain automatically. (Optional) -policy object_id The default policy to use for the response unless the client explicitly requires a particular TSA policy. The OID can be specified either in dotted notation or with its name. Overrides the default_policy config file option. (Optional) -in response.tsr Specifies a previously created time stamp response or time stamp token (if -token_in is also specified) in DER format that will be written to the output file. This option does not require a request, it is useful e.g. when you need to examine the content of a response or token or you want to extract the time stamp token from a response. If the input is a token and the output is a time stamp response a default granted status info is added to the token. (Optional) -token_in This flag can be used together with the -in option and indicates that the input is a DER encoded time stamp token (ContentInfo) instead of a time stamp response (TimeStampResp). (Optional) -out response.tsr The response is written to this file. The format and content of the file depends on other options (see -text, -token_out). The default is stdout. (Optional) -token_out The output is a time stamp token (ContentInfo) instead of time stamp response (TimeStampResp). (Optional) -text If this option is specified the output is human-readable text format instead of DER. (Optional) -engine id Specifying an engine (by its unique id string) will cause ts to attempt to obtain a functional reference to the specified engine, thus initialising it if needed. The engine will then be set as the default for all available algorithms. Default is builtin. (Optional)
The -verify command is for verifying if a time stamp response or time stamp token is valid and matches a particular time stamp request or data file. The -verify command does not use the configuration file.
-data file_to_hash The response or token must be verified against file_to_hash. The file is hashed with the message digest algorithm specified in the token. The -digest and -queryfile options must not be specified with this one. (Optional) -digest digest_bytes The response or token must be verified against the message digest specified with this option. The number of bytes must match the message digest algorithm specified in the token. The -data and -queryfile options must not be specified with this one. (Optional) -queryfile request.tsq The original time stamp request in DER format. The -data and -digest options must not be specified with this one. (Optional) -in response.tsr The time stamp response that needs to be verified in DER format. (Mandatory) -token_in This flag can be used together with the -in option and indicates that the input is a DER encoded time stamp token (ContentInfo) instead of a time stamp response (TimeStampResp). (Optional) -CApath trusted_cert_path The name of the directory containing the trused CA certificates of the client. See the similar option of verify(1) for additional details. Either this option or -CAfile must be specified. (Optional) -CAfile trusted_certs.pem The name of the file containing a set of trusted self-signed CA certificates in PEM format. See the similar option of verify(1) for additional details. Either this option or -CApath must be specified. (Optional) -untrusted cert_file.pem Set of additional untrusted certificates in PEM format which may be needed when building the certificate chain for the TSAs signing certificate. This file must contain the TSA signing certificate and all intermediate CA certificates unless the response includes them. (Optional)
The -query and -reply commands make use of a configuration file defined by the OPENSSL_CONF environment variable. See config(5) for a general description of the syntax of the config file. The -query command uses only the symbolic OID names section and it can work without it. However, the -reply command needs the config file for its operation.
When there is a command line switch equivalent of a variable the switch always overrides the settings in the config file.
tsa section, default_tsa This is the main section and it specifies the name of another section that contains all the options for the -reply command. This default section can be overridden with the -section command line switch. (Optional) oid_file See ca(1) for description. (Optional) oid_section See ca(1) for description. (Optional) RANDFILE See ca(1) for description. (Optional) serial The name of the file containing the hexadecimal serial number of the last time stamp response created. This number is incremented by 1 for each response. If the file does not exist at the time of response generation a new file is created with serial number 1. (Mandatory) crypto_device Specifies the OpenSSL engine that will be set as the default for all available algorithms. The default value is builtin, you can specify any other engines supported by OpenSSL (e.g. use chil for the NCipher HSM). (Optional) signer_cert TSA signing certificate in PEM format. The same as the -signer command line option. (Optional) certs A file containing a set of PEM encoded certificates that need to be included in the response. The same as the -chain command line option. (Optional) signer_key The private key of the TSA in PEM format. The same as the -inkey command line option. (Optional) default_policy The default policy to use when the request does not mandate any policy. The same as the -policy command line option. (Optional) other_policies Comma separated list of policies that are also acceptable by the TSA and used only if the request explicitly specifies one of them. (Optional) digests The list of message digest algorithms that the TSA accepts. At least one algorithm must be specified. (Mandatory) accuracy The accuracy of the time source of the TSA in seconds, milliseconds and microseconds. E.g. secs:1, millisecs:500, microsecs:100. If any of the components is missing zero is assumed for that field. (Optional) clock_precision_digits Specifies the maximum number of digits, which represent the fraction of seconds, that need to be included in the time field. The trailing zeroes must be removed from the time, so there might actually be fewer digits, or no fraction of seconds at all. Supported only on UNIX platforms. The maximum value is 6, default is 0. (Optional) ordering If this option is yes the responses generated by this TSA can always be ordered, even if the time difference between two responses is less than the sum of their accuracies. Default is no. (Optional) tsa_name Set this option to yes if the subject name of the TSA must be included in the TSA name field of the response. Default is no. (Optional) ess_cert_id_chain The SignedData objects created by the TSA always contain the certificate identifier of the signing certificate in a signed attribute (see RFC 2634, Enhanced Security Services). If this option is set to yes and either the certs variable or the -chain option is specified then the certificate identifiers of the chain will also be included in the SigningCertificate signed attribute. If this variable is set to no, only the signing certificate identifier is included. Default is no. (Optional)
OPENSSL_CONF contains the path of the configuration file and can be overridden by the -config command line option.
All the examples below presume that OPENSSL_CONF is set to a proper configuration file, e.g. the example configuration file openssl/apps/openssl.cnf will do.
To create a time stamp request for design1.txt with SHA-1 without nonce and policy and no certificate is required in the response:
openssl ts -query -data design1.txt -no_nonce \ -out design1.tsq
To create a similar time stamp request with specifying the message imprint explicitly:
openssl ts -query -digest b7e5d3f93198b38379852f2c04e78d73abdd0f4b \ -no_nonce -out design1.tsq
To print the content of the previous request in human readable format:
openssl ts -query -in design1.tsq -text
To create a time stamp request which includes the MD-5 digest of design2.txt, requests the signer certificate and nonce, specifies a policy id (assuming the tsa_policy1 name is defined in the OID section of the config file):
openssl ts -query -data design2.txt -md5 \ -policy tsa_policy1 -cert -out design2.tsq
Before generating a response a signing certificate must be created for the TSA that contains the timeStamping critical extended key usage extension without any other key usage extensions. You can add the extendedKeyUsage = critical,timeStamping line to the user certificate section of the config file to generate a proper certificate. See req(1), ca(1), x509(1) for instructions. The examples below assume that cacert.pem contains the certificate of the CA, tsacert.pem is the signing certificate issued by cacert.pem and tsakey.pem is the private key of the TSA.
To create a time stamp response for a request:
openssl ts -reply -queryfile design1.tsq -inkey tsakey.pem \ -signer tsacert.pem -out design1.tsr
If you want to use the settings in the config file you could just write:
openssl ts -reply -queryfile design1.tsq -out design1.tsr
To print a time stamp reply to stdout in human readable format:
openssl ts -reply -in design1.tsr -text
To create a time stamp token instead of time stamp response:
openssl ts -reply -queryfile design1.tsq -out design1_token.der -token_out
To print a time stamp token to stdout in human readable format:
openssl ts -reply -in design1_token.der -token_in -text -token_out
To extract the time stamp token from a response:
openssl ts -reply -in design1.tsr -out design1_token.der -token_out
To add granted status info to a time stamp token thereby creating a valid response:
openssl ts -reply -in design1_token.der -token_in -out design1.tsr
To verify a time stamp reply against a request:
openssl ts -verify -queryfile design1.tsq -in design1.tsr \ -CAfile cacert.pem -untrusted tsacert.pem
To verify a time stamp reply that includes the certificate chain:
openssl ts -verify -queryfile design2.tsq -in design2.tsr \ -CAfile cacert.pem
To verify a time stamp token against the original data file:
openssl ts -verify -data design2.txt -in design2.tsr \
To verify a time stamp token against a message imprint:
openssl ts -verify -digest b7e5d3f93198b38379852f2c04e78d73abdd0f4b \
-in design2.tsr -CAfile cacert.pem
You could also look at the test directory for more examples.
If you find any bugs or you have suggestions please write to Zoltan Glozik <email@example.com>. Known issues:
o No support for time stamps over SMTP, though it is quite easy to implement an automatic e-mail based TSA with procmail(1) and perl(1). HTTP server support is provided in the form of a separate apache module. HTTP client support is provided by tsget(1). Pure TCP/IP protocol is not supported. o The file containing the last serial number of the TSA is not locked when being read or written. This is a problem if more than one instance of openssl(1) is trying to create a time stamp response at the same time. This is not an issue when using the apache server module, it does proper locking. o Look for the FIXME word in the source files. o The source code should really be reviewed by somebody else, too. o More testing is needed, I have done only some basic tests (see test/testtsa).
Zoltan Glozik <firstname.lastname@example.org>, OpenTSA project (http://www.opentsa.org)
tsget(1), openssl(1), req(1), x509(1), ca(1), genrsa(1), config(5)