- Unix, Linux Command

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req - PKCS#10 certificate request and certificate generating utility.


openssl req [-inform PEM|DER] [-outform PEM|DER] [-in filename] [-passin arg] [-out filename] [-passout arg] [-text] [-pubkey] [-noout] [-verify] [-modulus] [-new] [-rand file(s)] [-newkey rsa:bits] [-newkey dsa:file] [-nodes] [-key filename] [-keyform PEM|DER] [-keyout filename] [-[md5|sha1|md2|mdc2]] [-config filename] [-subj arg] [-multivalue-rdn] [-x509] [-days n] [-set_serial n] [-asn1-kludge] [-newhdr] [-extensions section] [-reqexts section] [-utf8] [-nameopt] [-batch] [-verbose] [-engine id]


The req command primarily creates and processes certificate requests in PKCS#10 format. It can additionally create self signed certificates for use as root CAs for example.


-inform DER|PEM This specifies the input format. The DER option uses an ASN1 DER encoded form compatible with the PKCS#10. The PEM form is the default format: it consists of the DER format base64 encoded with additional header and footer lines.
-outform DER|PEM This specifies the output format, the options have the same meaning as the -inform option.
-in filename This specifies the input filename to read a request from or standard input if this option is not specified. A request is only read if the creation options (-new and -newkey) are not specified.
-passin arg the input file password source. For more information about the format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
-out filename This specifies the output filename to write to or standard output by default.
-passout arg the output file password source. For more information about the format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
-text prints out the certificate request in text form.
-pubkey outputs the public key.
-noout this option prevents output of the encoded version of the request.
-modulus this option prints out the value of the modulus of the public key contained in the request.
-verify verifies the signature on the request.
-new this option generates a new certificate request. It will prompt the user for the relevant field values. The actual fields prompted for and their maximum and minimum sizes are specified in the configuration file and any requested extensions.

If the -key option is not used it will generate a new RSA private key using information specified in the configuration file.

-rand file(s) a file or files containing random data used to seed the random number generator, or an EGD socket (see RAND_egd(3)). Multiple files can be specified separated by a OS-dependent character. The separator is ; for MS-Windows, , for OpenVMS, and : for all others.
-newkey arg this option creates a new certificate request and a new private key. The argument takes one of two forms. rsa:nbits, where nbits is the number of bits, generates an RSA key nbits in size. dsa:filename generates a DSA key using the parameters in the file filename.
-key filename This specifies the file to read the private key from. It also accepts PKCS#8 format private keys for PEM format files.
-keyform PEM|DER the format of the private key file specified in the -key argument. PEM is the default.
-keyout filename this gives the filename to write the newly created private key to. If this option is not specified then the filename present in the configuration file is used.
-nodes if this option is specified then if a private key is created it will not be encrypted.
-[md5|sha1|md2|mdc2] this specifies the message digest to sign the request with. This overrides the digest algorithm specified in the configuration file. This option is ignored for DSA requests: they always use SHA1.
-config filename this allows an alternative configuration file to be specified, this overrides the compile time filename or any specified in the OPENSSL_CONF environment variable.
-subj arg sets subject name for new request or supersedes the subject name when processing a request. The arg must be formatted as /type0=value0/type1=value1/type2=..., characters may be escaped by \ (backslash), no spaces are skipped.
-multivalue-rdn this option causes the -subj argument to be interpreted with full support for multivalued RDNs. Example:

/DC=org/DC=OpenSSL/DC=users/UID=123456+CN=John Doe

If -multi-rdn is not used then the UID value is 123456+CN=John Doe.

-x509 this option outputs a self signed certificate instead of a certificate request. This is typically used to generate a test certificate or a self signed root CA. The extensions added to the certificate (if any) are specified in the configuration file. Unless specified using the set_serial option 0 will be used for the serial number.
-days n when the -x509 option is being used this specifies the number of days to certify the certificate for. The default is 30 days.
-set_serial n serial number to use when outputting a self signed certificate. This may be specified as a decimal value or a hex value if preceded by 0x. It is possible to use negative serial numbers but this is not recommended.
-extensions section
-reqexts section these options specify alternative sections to include certificate extensions (if the -x509 option is present) or certificate request extensions. This allows several different sections to be used in the same configuration file to specify requests for a variety of purposes.
-utf8 this option causes field values to be interpreted as UTF8 strings, by default they are interpreted as ASCII. This means that the field values, whether prompted from a terminal or obtained from a configuration file, must be valid UTF8 strings.
-nameopt option option which determines how the subject or issuer names are displayed. The option argument can be a single option or multiple options separated by commas. Alternatively the -nameopt switch may be used more than once to set multiple options. See the x509(1) manual page for details.
-asn1-kludge by default the req command outputs certificate requests containing no attributes in the correct PKCS#10 format. However certain CAs will only accept requests containing no attributes in an invalid form: this option produces this invalid format.

More precisely the Attributes in a PKCS#10 certificate request are defined as a SET OF Attribute. They are not OPTIONAL so if no attributes are present then they should be encoded as an empty SET OF. The invalid form does not include the empty SET OF whereas the correct form does.

It should be noted that very few CAs still require the use of this option.

-newhdr Adds the word NEW to the PEM file header and footer lines on the outputed request. Some software (Netscape certificate server) and some CAs need this.
-batch non-interactive mode.
-verbose print extra details about the operations being performed.
-engine id specifying an engine (by it’s unique id string) will cause req 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.


The configuration options are specified in the req section of the configuration file. As with all configuration files if no value is specified in the specific section (i.e. req) then the initial unnamed or default section is searched too.

The options available are described in detail below.

input_password output_password The passwords for the input private key file (if present) and the output private key file (if one will be created). The command line options passin and passout override the configuration file values.
default_bits This specifies the default key size in bits. If not specified then 512 is used. It is used if the -new option is used. It can be overridden by using the -newkey option.
default_keyfile This is the default filename to write a private key to. If not specified the key is written to standard output. This can be overridden by the -keyout option.
oid_file This specifies a file containing additional OBJECT IDENTIFIERS. Each line of the file should consist of the numerical form of the object identifier followed by white space then the short name followed by white space and finally the long name.
oid_section This specifies a section in the configuration file containing extra object identifiers. Each line should consist of the short name of the object identifier followed by = and the numerical form. The short and long names are the same when this option is used.
RANDFILE This specifies a filename in which random number seed information is placed and read from, or an EGD socket (see RAND_egd(3)). It is used for private key generation.
encrypt_key If this is set to no then if a private key is generated it is not encrypted. This is equivalent to the -nodes command line option. For compatibility encrypt_rsa_key is an equivalent option.
default_md This option specifies the digest algorithm to use. Possible values include md5 sha1 mdc2. If not present then MD5 is used. This option can be overridden on the command line.
string_mask This option masks out the use of certain string types in certain fields. Most users will not need to change this option.

It can be set to several values default which is also the default option uses PrintableStrings, T61Strings and BMPStrings if the pkix value is used then only PrintableStrings and BMPStrings will be used. This follows the PKIX recommendation in RFC2459. If the utf8only option is used then only UTF8Strings will be used: this is the PKIX recommendation in RFC2459 after 2003. Finally the nombstr option just uses PrintableStrings and T61Strings: certain software has problems with BMPStrings and UTF8Strings: in particular Netscape.

req_extensions this specifies the configuration file section containing a list of extensions to add to the certificate request. It can be overridden by the -reqexts command line switch.
x509_extensions this specifies the configuration file section containing a list of extensions to add to certificate generated when the -x509 switch is used. It can be overridden by the -extensions command line switch.
prompt if set to the value no this disables prompting of certificate fields and just takes values from the config file directly. It also changes the expected format of the distinguished_name and attributes sections.
utf8 if set to the value yes then field values to be interpreted as UTF8 strings, by default they are interpreted as ASCII. This means that the field values, whether prompted from a terminal or obtained from a configuration file, must be valid UTF8 strings.
attributes this specifies the section containing any request attributes: its format is the same as distinguished_name. Typically these may contain the challengePassword or unstructuredName types. They are currently ignored by OpenSSL’s request signing utilities but some CAs might want them.
distinguished_name This specifies the section containing the distinguished name fields to prompt for when generating a certificate or certificate request. The format is described in the next section.


There are two separate formats for the distinguished name and attribute sections. If the prompt option is set to no then these sections just consist of field names and values: for example,

 CN=My Name
 OU=My Organization

This allows external programs (e.g. GUI based) to generate a template file with all the field names and values and just pass it to req. An example of this kind of configuration file is contained in the EXAMPLES section.

Alternatively if the prompt option is absent or not set to no then the file contains field prompting information. It consists of lines of the form:

 fieldName_default="default field value"
 fieldName_min= 2
 fieldName_max= 4

fieldName is the field name being used, for example commonName (or CN). The prompt string is used to ask the user to enter the relevant details. If the user enters nothing then the default value is used if no default value is present then the field is omitted. A field can still be omitted if a default value is present if the user just enters the ’.’ character.

The number of characters entered must be between the fieldName_min and fieldName_max limits: there may be additional restrictions based on the field being used (for example countryName can only ever be two characters long and must fit in a PrintableString).

Some fields (such as organizationName) can be used more than once in a DN. This presents a problem because configuration files will not recognize the same name occurring twice. To avoid this problem if the fieldName contains some characters followed by a full stop they will be ignored. So for example a second organizationName can be input by calling it 1.organizationName.

The actual permitted field names are any object identifier short or long names. These are compiled into OpenSSL and include the usual values such as commonName, countryName, localityName, organizationName, organizationUnitName, stateOrProvinceName. Additionally emailAddress is include as well as name, surname, givenName initials and dnQualifier.

Additional object identifiers can be defined with the oid_file or oid_section options in the configuration file. Any additional fields will be treated as though they were a DirectoryString.


Examine and verify certificate request:

 openssl req -in req.pem -text -verify -noout

Create a private key and then generate a certificate request from it:

 openssl genrsa -out key.pem 1024
 openssl req -new -key key.pem -out req.pem

The same but just using req:

 openssl req -newkey rsa:1024 -keyout key.pem -out req.pem

Generate a self signed root certificate:

 openssl req -x509 -newkey rsa:1024 -keyout key.pem -out req.pem

Example of a file pointed to by the oid_file option:        shortName       A longer Name        otherName       Other longer Name

Example of a section pointed to by oid_section making use of variable expansion:


Sample configuration file prompting for field values:

 [ req ]
 default_bits           = 1024
 default_keyfile        = privkey.pem
 distinguished_name     = req_distinguished_name
 attributes             = req_attributes
 x509_extensions        = v3_ca

 dirstring_type = nobmp

 [ req_distinguished_name ]
 countryName                    = Country Name (2 letter code)
 countryName_default            = AU
 countryName_min                = 2
 countryName_max                = 2

 localityName                   = Locality Name (eg, city)

 organizationalUnitName         = Organizational Unit Name (eg, section)

 commonName                     = Common Name (eg, YOUR name)
 commonName_max                 = 64

 emailAddress                   = Email Address
 emailAddress_max               = 40

 [ req_attributes ]
 challengePassword              = A challenge password
 challengePassword_min          = 4
 challengePassword_max          = 20

 [ v3_ca ]

 basicConstraints = CA:true

Sample configuration containing all field values:

 RANDFILE               = $ENV::HOME/.rnd

 [ req ]
 default_bits           = 1024
 default_keyfile        = keyfile.pem
 distinguished_name     = req_distinguished_name
 attributes             = req_attributes
 prompt                 = no
 output_password        = mypass

 [ req_distinguished_name ]
 C                      = GB
 ST                     = Test State or Province
 L                      = Test Locality
 O                      = Organization Name
 OU                     = Organizational Unit Name
 CN                     = Common Name
 emailAddress           = test@email.address

 [ req_attributes ]
 challengePassword              = A challenge password


The header and footer lines in the PEM format are normally:


some software (some versions of Netscape certificate server) instead needs:


which is produced with the -newhdr option but is otherwise compatible. Either form is accepted transparently on input.

The certificate requests generated by Xenroll with MSIE have extensions added. It includes the keyUsage extension which determines the type of key (signature only or general purpose) and any additional OIDs entered by the script in an extendedKeyUsage extension.


The following messages are frequently asked about:

        Using configuration from /some/path/openssl.cnf
        Unable to load config info

This is followed some time later by...

        unable to find ’distinguished_name’ in config
        problems making Certificate Request

The first error message is the clue: it can’t find the configuration file! Certain operations (like examining a certificate request) don’t need a configuration file so its use isn’t enforced. Generation of certificates or requests however does need a configuration file. This could be regarded as a bug.

Another puzzling message is this:


this is displayed when no attributes are present and the request includes the correct empty SET OF structure (the DER encoding of which is 0xa0 0x00). If you just see:


then the SET OF is missing and the encoding is technically invalid (but it is tolerated). See the description of the command line option -asn1-kludge for more information.


The variable OPENSSL_CONF if defined allows an alternative configuration file location to be specified, it will be overridden by the -config command line switch if it is present. For compatibility reasons the SSLEAY_CONF environment variable serves the same purpose but its use is discouraged.


OpenSSL’s handling of T61Strings (aka TeletexStrings) is broken: it effectively treats them as ISO-8859-1 (Latin 1), Netscape and MSIE have similar behaviour. This can cause problems if you need characters that aren’t available in PrintableStrings and you don’t want to or can’t use BMPStrings.

As a consequence of the T61String handling the only correct way to represent accented characters in OpenSSL is to use a BMPString: unfortunately Netscape currently chokes on these. If you have to use accented characters with Netscape and MSIE then you currently need to use the invalid T61String form.

The current prompting is not very friendly. It doesn’t allow you to confirm what you’ve just entered. Other things like extensions in certificate requests are statically defined in the configuration file. Some of these: like an email address in subjectAltName should be input by the user.


x509(1), ca(1), genrsa(1), gendsa(1), config(5)
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