Command Line Utilities

From OpenSSLWiki
Revision as of 21:11, 30 July 2019 by Jflopezfernandez (talk | contribs) (Added section on 1-step ecc key generation, as per Matt's suggestion on the discussion page)

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

The openssl program provides a rich variety of commands, each of which often has a wealth of options and arguments. Many commands use an external configuration file for some or all of their arguments and have a -config option to specify that file. The environment variable OPENSSL_CONF can be used to specify the location of the configuration file. If the environment variable is not specified, a default file is created in the default certificate storage area called openssl.cnf. The settings in this default configuration file depend on the flags set when the version of OpenSSL being used was built.

This article is an overview of the available tools provided by openssl. For all of the details on usage and implementation, you can find the manpages which are automatically generated from the source code at the official OpenSSL project home. Likewise, the source code itself may be found on the OpenSSL project home page, as well as on the OpenSSL Github. The main OpenSSL site also includes an overview of the command-line utilities, as well as links to all of their respective documentation.

Getting Started[edit]

The entry point for the OpenSSL library is the openssl binary, usually /usr/bin/openssl on Linux. The general syntax for calling openssl is as follows:

$ openssl command [ command_options ] [ command_arguments ]

Alternatively, you can call openssl without arguments to enter the interactive mode prompt. You may then enter commands directly, exiting with either a quit command or by issuing a termination signal with either Ctrl+C or Ctrl+D. The following is a sample interactive session in which the user invokes the prime command twice before using the quit command to terminate the session.

OpenSSL> prime -generate -bits 24
13467269
OpenSSL> prime -generate -bits 24
16651079
OpenSSL> quit

Basic Tasks[edit]

This section is a brief tutorial on performing the most basic tasks using OpenSSL. For a detailed explanation of the rationale behind the syntax and semantics of the commands shown here, see the section on Commands.

Getting Help[edit]

As mentioned previously, the general syntax of a command is openssl command [ command_options ] [ command_arguments ]. The help command is no different, but it does have its idiosyncrasies. To view the top-level help menu, you can call openssl as follows.

$ openssl help

This query will print all of the available commands, like so:

Standard commands
asn1parse         ca                ciphers           cms               
crl               crl2pkcs7         dgst              dhparam           
dsa               dsaparam          ec                ecparam
...

Note the above output was truncated, so only the first four lines of output are shown.

A help menu for each command may be requested in two different ways. First, the same command used above may be repeated, followed by the name of the command to print help for.

$ openssl help genpkey

The program will then display the valid options for the given command.

$ openssl help genpkey
Usage: genpkey [options]
Valid options are:
 -help              Display this summary
 -out outfile       Output file
 -outform PEM|DER   output format (DER or PEM)
 -pass val          Output file pass phrase source
 -paramfile infile  Parameters file
 -algorithm val     The public key algorithm
 -pkeyopt val       Set the public key algorithm option as opt:value
 -genparam          Generate parameters, not key
 -text              Print the in text
 -*                 Cipher to use to encrypt the key
 -engine val        Use engine, possibly a hardware device
Order of options may be important!  See the documentation.

The second way of requesting the help menu for a particular command is by using the first option in the output shown above, namely openssl command -help. Both commands will yield the same output; the help menu displayed will be exactly the same.

$ openssl genpkey -help
Usage: genpkey [options]
Valid options are:
 -help              Display this summary
 -out outfile       Output file
 -outform PEM|DER   output format (DER or PEM)
 -pass val          Output file pass phrase source
 -paramfile infile  Parameters file
 -algorithm val     The public key algorithm
 -pkeyopt val       Set the public key algorithm option as opt:value
 -genparam          Generate parameters, not key
 -text              Print the in text
 -*                 Cipher to use to encrypt the key
 -engine val        Use engine, possibly a hardware device
Order of options may be important!  See the documentation.

For additional information on the usage of a particular command, the project manpages are a great source of information. Another excellent source of information is the project perldocs. perldoc is a utility included with most if not all Perl distributions, and it's capable of displaying documentation information in a variety of formats, one of which is as manpages. Not surprisingly, the project documentation is generated from the pod files located in the doc directory of the source code.

Getting Library Version Information[edit]

$ openssl version
OpenSSL 1.1.1c  28 May 2019

As mentioned above, the version command's help menu may be queried for additional options like so:

$ openssl version -help
Usage: version [options]
Valid options are:
 -help  Display this summary
 -a     Show all data
 -b     Show build date
 -d     Show configuration directory
 -e     Show engines directory
 -f     Show compiler flags used
 -o     Show some internal datatype options
 -p     Show target build platform
 -r     Show random seeding options
 -v     Show library version

Using the -a option to show all version information yields the following output on my current machine:

$ openssl version -a
OpenSSL 1.1.1c  28 May 2019
built on: Tue May 28 16:23:39 2019 UTC
platform: linux-x86_64
options:  bn(64,64) rc4(16x,int) des(int) idea(int) blowfish(ptr) 
compiler: gcc -fPIC -pthread -m64 -Wa,--noexecstack -march=x86-64 -mtune=generic -O2 -pipe -fno-plt -Wa,--noexecstack -D_FORTIFY_SOURCE=2 -march=x86-64 -mtune=generic -O2 -pipe -fno-plt -Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -DOPENSSL_USE_NODELETE -DL_ENDIAN -DOPENSSL_PIC -DOPENSSL_CPUID_OBJ -DOPENSSL_IA32_SSE2 -DOPENSSL_BN_ASM_MONT -DOPENSSL_BN_ASM_MONT5 -DOPENSSL_BN_ASM_GF2m -DSHA1_ASM -DSHA256_ASM -DSHA512_ASM -DKECCAK1600_ASM -DRC4_ASM -DMD5_ASM -DAES_ASM -DVPAES_ASM -DBSAES_ASM -DGHASH_ASM -DECP_NISTZ256_ASM -DX25519_ASM -DPOLY1305_ASM -DNDEBUG -D_FORTIFY_SOURCE=2
OPENSSLDIR: "/etc/ssl"
ENGINESDIR: "/usr/lib/engines-1.1"
Seeding source: os-specific

Generating an RSA Private Key[edit]

Generating a private key can be done in a variety of different ways depending on the type of key, algorithm, bits, and other options your specific use case may require. In this example, we are generating a private key using RSA and a key size of 2048 bits.

$ openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out private-key.pem

To generate a password protected private key, the previous command may be slightly amended as follows:

$ openssl genpkey -aes256 -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out private-key.pem

The addition of the -aes256 option specifies the cipher to use to encrypt the private key file. For a list of available ciphers in the library, you can run the following command:

$ openssl list -cipher-algorithms

With your private key in hand, you can use the following command to see the key's details, such as its modulus and its constituent primes. Remember to change the name of the input file to the file name of your private key.

$ openssl pkey -in private-key.pem -text

The above command yields the following output in my specific case. Your output will differ but should be structurally similar.

-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----
RSA Private-Key: (2048 bit, 2 primes)
modulus:
    00:d9:0f:a2:0c:2d:11:64:e0:26:85:c3:4a:e1:46:
    27:a7:c2:e1:39:11:9e:b1:14:4f:1e:dc:2e:53:56:
    2d:7e:77:d1:27:86:2d:fc:46:09:30:0f:b5:25:5b:
    13:c4:e8:05:a1:a7:94:f7:91:fa:c5:59:d6:a4:d6:
    56:45:54:fa:7b:fd:bb:4e:28:b8:ca:52:bb:b5:e6:
    72:e8:03:80:0a:62:dc:fd:5b:d3:e1:b0:cd:1d:cb:
    32:dc:e8:54:3a:2b:84:5e:41:a9:b9:a4:70:aa:23:
    6c:c5:f3:63:30:13:e7:88:01:db:af:ba:ac:a8:40:
    b2:a2:23:ad:3c:10:0a:d6:66:a0:ed:31:4a:41:27:
    3b:f4:51:51:18:bd:17:67:31:6a:42:c1:fc:e9:23:
    e8:4f:27:2c:15:09:c4:e5:34:24:ff:72:d1:a0:04:
    ac:88:c7:e7:43:b9:9e:db:47:d3:0d:99:25:bb:1a:
    b7:89:11:b4:c7:f9:1d:77:c5:3d:dd:77:f2:42:91:
    ad:7e:2d:80:a5:e2:1d:2a:a1:68:45:3e:13:a4:bd:
    0c:e6:99:2c:d4:99:99:40:95:30:d0:2e:fd:9e:01:
    d2:48:ad:07:2c:9c:a6:77:4a:c2:0e:08:2f:f7:22:
    9a:b0:4b:3a:62:77:7f:08:96:5e:0e:c4:7e:97:22:
    b5:45
publicExponent: 65537 (0x10001)
privateExponent:
    00:9d:8c:0b:42:6b:33:c4:d4:2d:21:c9:ad:ff:f4:
    bb:b3:b8:6f:60:cc:b9:32:2e:5b:7f:3a:b1:25:2b:
    d7:b9:83:9d:fb:e2:18:5e:93:36:f7:fb:6e:af:be:
    7b:8a:e0:1d:b6:47:bc:88:35:1c:9f:41:a5:d9:de:
    f8:9f:3a:1e:d5:00:45:83:65:6b:3a:ee:f1:f0:05:
    64:41:a2:c8:bc:c1:25:45:7f:f1:3a:4e:e9:92:46:
    7a:94:7c:cd:25:ab:90:58:19:b0:e7:5d:c3:a8:ba:
    2d:a9:40:0f:2e:46:44:37:23:a2:20:da:8d:97:51:
    de:56:71:2e:bb:f9:a8:e4:14:23:5b:ca:4d:fe:19:
    b3:64:e5:de:09:da:27:f2:25:d6:00:47:21:0f:56:
    f7:15:07:f2:33:c1:23:08:f9:d6:25:f0:0a:1f:07:
    d0:18:83:3e:f1:64:53:b7:07:20:50:8f:b0:98:46:
    b0:6a:7a:39:2d:ee:4b:0c:10:b9:21:3e:36:a6:ee:
    3d:f5:62:97:2b:02:73:08:19:76:e9:27:ca:2a:34:
    40:ed:58:7c:c0:4b:eb:e5:e8:28:4f:db:14:7b:27:
    37:e1:73:cd:cc:d0:83:db:16:ca:2c:15:47:ed:c4:
    78:8f:64:a7:82:52:12:53:61:da:7a:86:f7:a8:b8:
    40:01
prime1:
    00:ef:a3:8b:50:6a:d2:84:76:f8:b1:aa:0f:69:89:
    c1:00:a2:c4:75:68:f9:2b:8f:37:25:d6:3a:05:26:
    dd:77:94:64:0d:b2:46:f0:4c:66:71:b7:d3:6a:cf:
    c1:19:d2:9c:e2:25:42:93:15:77:ca:cc:4a:9d:7d:
    7c:3d:fc:40:4c:70:cb:2f:c3:4c:6b:e8:06:81:96:
    39:a1:32:94:b2:b5:c4:a5:2d:77:d8:78:42:27:d4:
    fd:2e:87:ac:42:34:5b:e2:43:99:1f:c3:ce:56:a9:
    ba:3b:85:df:94:2b:74:cb:5f:8c:d5:e4:07:23:53:
    4f:3b:d0:a6:3c:18:28:b8:45
prime2:
    00:e7:e1:78:49:2f:11:33:26:11:91:4f:e4:c7:5f:
    79:7f:08:74:86:16:8e:12:5c:eb:13:c9:99:a2:ed:
    cd:14:bf:d7:4f:af:fd:b7:ed:be:ee:c3:13:ba:24:
    02:3f:dc:c8:6b:ab:3e:fe:ba:d7:76:35:ad:ad:37:
    03:a7:85:a5:0c:84:da:b3:45:14:81:98:6f:61:50:
    50:04:5e:2f:84:7c:48:57:02:71:9d:3f:46:c2:2e:
    17:33:52:65:16:65:47:a1:f5:83:ef:53:fa:0d:17:
    bb:8d:25:91:4b:70:ae:8c:fd:c0:13:db:e6:a5:63:
    31:b4:4d:43:f6:a2:e2:59:01
exponent1:
    78:e3:92:f3:15:80:6f:ac:a8:d6:cf:88:88:e0:22:
    4a:14:d2:70:bc:6c:fe:89:77:f3:91:77:a1:83:b2:
    b3:91:5b:4c:01:84:81:d2:b8:d7:63:39:b7:27:69:
    2d:82:ae:fb:f2:79:fc:43:17:34:6a:0c:b6:18:48:
    a5:e8:6b:f3:63:ef:4c:80:04:3c:67:47:68:f6:04:
    ca:89:fe:b3:8c:b8:cf:ee:f9:07:6d:db:49:c6:cb:
    96:3e:81:2a:c0:c9:1d:82:a6:6b:7c:d6:c9:a7:43:
    b8:a5:57:5d:a2:f2:7f:6a:0b:5d:17:74:76:60:9f:
    96:f8:31:f4:1c:e7:e5:d5
exponent2:
    59:cc:73:6c:c4:11:81:21:69:04:41:50:73:f5:81:
    73:b4:ae:8b:8f:08:8e:0b:f5:ed:bf:d1:03:cb:db:
    f4:01:27:3c:f1:06:ec:c7:e1:7d:4d:86:c2:3b:57:
    b3:ab:a8:e2:29:7b:47:e2:cb:b6:37:ab:7e:bd:23:
    69:28:d4:76:38:ad:09:67:e3:3d:1c:ef:65:5c:58:
    e0:98:29:06:c1:aa:b2:27:7c:20:4d:74:f5:96:2b:
    dd:f0:36:bd:a9:93:48:21:70:6a:aa:b6:d7:83:2d:
    5a:c8:05:b0:95:7e:c3:93:31:63:7f:71:9e:f2:ff:
    38:b8:03:6d:ec:3e:84:01
coefficient:
    10:fc:dc:22:33:b2:a0:1f:7b:3f:37:7b:88:d8:a6:
    1a:29:fc:46:4c:17:22:21:46:48:7a:3c:bc:08:7b:
    e0:22:81:36:89:13:84:ce:74:39:43:66:e5:3d:9e:
    27:88:6e:cc:fa:68:c1:0f:88:0f:59:81:e4:48:c4:
    6a:2f:67:25:8f:65:97:77:14:a5:ac:22:20:85:bf:
    ea:e1:93:1f:25:df:bd:95:8d:b6:a1:18:5e:b5:49:
    e9:f7:03:68:a7:16:e3:2d:dc:a6:53:63:fd:22:5a:
    05:6f:07:5e:c5:bb:60:61:d6:df:31:ec:83:2e:c4:
    38:03:b3:3f:09:66:f6:81

Keep in mind the above key was generated solely for pedagogical purposes; never give anyone access to your private keys.

Generating a Public Key[edit]

Having previously generated your private key, you may generate the corresponding public key using the following command.

$ openssl pkey -in private-key.pem -out public-key.pem -pubout

You may once again view the key details, using a slightly different command this time.

$ openssl pkey -in public-key.pem -pubin -text

The output for the public key will be shorter, as it carries much less information, and it will look something like this.

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA2Q+iDC0RZOAmhcNK4UYn
p8LhORGesRRPHtwuU1YtfnfRJ4Yt/EYJMA+1JVsTxOgFoaeU95H6xVnWpNZWRVT6
e/27Tii4ylK7teZy6AOACmLc/VvT4bDNHcsy3OhUOiuEXkGpuaRwqiNsxfNjMBPn
iAHbr7qsqECyoiOtPBAK1mag7TFKQSc79FFRGL0XZzFqQsH86SPoTycsFQnE5TQk
/3LRoASsiMfnQ7me20fTDZkluxq3iRG0x/kdd8U93XfyQpGtfi2ApeIdKqFoRT4T
pL0M5pks1JmZQJUw0C79ngHSSK0HLJymd0rCDggv9yKasEs6Ynd/CJZeDsR+lyK1
RQIDAQAB
-----END PUBLIC KEY-----
RSA Public-Key: (2048 bit)
Modulus:
    00:d9:0f:a2:0c:2d:11:64:e0:26:85:c3:4a:e1:46:
    27:a7:c2:e1:39:11:9e:b1:14:4f:1e:dc:2e:53:56:
    2d:7e:77:d1:27:86:2d:fc:46:09:30:0f:b5:25:5b:
    13:c4:e8:05:a1:a7:94:f7:91:fa:c5:59:d6:a4:d6:
    56:45:54:fa:7b:fd:bb:4e:28:b8:ca:52:bb:b5:e6:
    72:e8:03:80:0a:62:dc:fd:5b:d3:e1:b0:cd:1d:cb:
    32:dc:e8:54:3a:2b:84:5e:41:a9:b9:a4:70:aa:23:
    6c:c5:f3:63:30:13:e7:88:01:db:af:ba:ac:a8:40:
    b2:a2:23:ad:3c:10:0a:d6:66:a0:ed:31:4a:41:27:
    3b:f4:51:51:18:bd:17:67:31:6a:42:c1:fc:e9:23:
    e8:4f:27:2c:15:09:c4:e5:34:24:ff:72:d1:a0:04:
    ac:88:c7:e7:43:b9:9e:db:47:d3:0d:99:25:bb:1a:
    b7:89:11:b4:c7:f9:1d:77:c5:3d:dd:77:f2:42:91:
    ad:7e:2d:80:a5:e2:1d:2a:a1:68:45:3e:13:a4:bd:
    0c:e6:99:2c:d4:99:99:40:95:30:d0:2e:fd:9e:01:
    d2:48:ad:07:2c:9c:a6:77:4a:c2:0e:08:2f:f7:22:
    9a:b0:4b:3a:62:77:7f:08:96:5e:0e:c4:7e:97:22:
    b5:45
Exponent: 65537 (0x10001)

For more information on generating keys, see the source code documentation, located in the doc/HOWTO/keys.txt file.

Generating Keys Based on Elliptic Curves[edit]

There are essentially two steps to generating a key:

  1. Generate the parameters for the specific curve you are using
  2. Use those parameters to generate the key

To see the list of curves instrinsically supported by openssl, you can use the -list_curves</t> option when calling the <tt>ecparam command.

$ openssl ecparam -list_curves
  secp112r1 : SECG/WTLS curve over a 112 bit prime field
  secp112r2 : SECG curve over a 112 bit prime field
  secp128r1 : SECG curve over a 128 bit prime field
  secp128r2 : SECG curve over a 128 bit prime field
  secp160k1 : SECG curve over a 160 bit prime field
  ...

For this example I will use the prime256v1 curve, which is an X9.62/SECG curve over a 256 bit prime field.

Generating the Curve Parameters[edit]

Having selected our curve, we now call ecparam to generate our parameters file.

$ openssl ecparam -name prime256v1 -out prime256v1.pem

Printing Parameters to Standard Out[edit]

You can print the generated curve parameters to the terminal output with the following command:

$ openssl ecparam -in prime256v1.pem -noout -text
ASN1 OID: prime256v1
NIST CURVE: P-256

Printing Parameters as C Code[edit]

Analogously, you may also output the generated curve parameters as C code. The parameters can then be loaded by calling the get_ec_group_XXX() function. To print the C code to the current terminal's output, the following command may be used:

$ openssl ecparam -in prime256v1.pem -noout -C

And here are the first few lines of the corresponding output:

EC_GROUP *get_ec_group_256(void)
{
    static unsigned char ec_p_256[] = {
        0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
        ...

Generating the Key[edit]

With the curve parameters in hand, we are now free to generate the key. Just as with the [#Generating an RSA Private Key|RSA] example above, we may optionally specify a cipher algorithm with which to encrypt the private key. The call to generate the key using the elliptic curve parameters generated in the example above looks like this:

$ openssl genpkey -aes256 -paramfile prime256v1.pem -out private-key.pem
Enter PEM pass phrase:
Verifying - Enter PEM pass phrase:

Putting it All Together[edit]

The process of generation a curve based on elliptic-curves can be streamlined by calling the genpkey command directly and specifying both the algorithm and the name of the curve to use for parameter generation. In it's simplest form, the command to generate a key based on the same curve as in the example above looks like this:

$ openssl genpkey -algorithm EC -pkeyopt ec_paramgen_curve:P-256

This command will result in the generated key being printed to the terminal's output.

$ openssl genpkey -algorithm EC -pkeyopt ec_paramgen_curve:P-256

-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgqqYoJGowXJ5/GTkB
SRLnBMNWLoQ2RM/QxrY+bfDDGRahRANCAASPY4eTANkwIIAWhh32eoFl2YFLJSWy
bdITdZ82O5JDpDijmGmJ2hepe5afek9WVqxMPYjmbTwMPO3xMGbqUiJD
-----END PRIVATE KEY-----

Remember that you can specify a cipher algorithm to encrypt the key with, which something you may or may not want to do, depending on your specific use case. Here is a slightly more complete example showing a key generated with a password and written to a specific output file.

$ openssl genpkey -aes256 -algorithm EC -pkeyopt ec_paramgen_curve:P-256 -out private-key.pem
Enter PEM pass phrase:
Verifying - Enter PEM pass phrase:

Just as with the previous example, you can use the pkey command to inspect your newly-generated key.

$ openssl pkey -in private-key.pem -text
Enter pass phrase for private-key.pem:
-----BEGIN PRIVATE KEY-----
MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQgEO7CxgTwi0hsjdbp
sXWuU2x2flLthxqXabYDOqOZCvuhRANCAAQVTLkeCBJdvMnqwZKYJxrPvTTuanrD
NkyAPQCARKsQ7bVrP6ky/5uAcAvjuZB0xKCcSp7roXLWRzD/y/ik8P5R
-----END PRIVATE KEY-----
Private-Key: (256 bit)
priv:
    10:ee:c2:c6:04:f0:8b:48:6c:8d:d6:e9:b1:75:ae:
    53:6c:76:7e:52:ed:87:1a:97:69:b6:03:3a:a3:99:
    0a:fb
pub:
    04:15:4c:b9:1e:08:12:5d:bc:c9:ea:c1:92:98:27:
    1a:cf:bd:34:ee:6a:7a:c3:36:4c:80:3d:00:80:44:
    ab:10:ed:b5:6b:3f:a9:32:ff:9b:80:70:0b:e3:b9:
    90:74:c4:a0:9c:4a:9e:eb:a1:72:d6:47:30:ff:cb:
    f8:a4:f0:fe:51
ASN1 OID: prime256v1
NIST CURVE: P-256

For more details on elliptic curve cryptography or key generation, check out the manpages.

Base64 Encoding Strings[edit]

For simple string encoding, you can use "here string" syntax with the base64 command as below. Intuitively, the -e flag specifies the action to be encoding.

$ openssl base64 -e <<< 'Welcome to openssl wiki'
V2VsY29tZSB0byBvcGVuc3NsIHdpa2kK

Similarly, the base64 command's -d flag may be used to indicate decoding mode.

$ openssl base64 -d <<< 'V2VsY29tZSB0byBvcGVuc3NsIHdpa2kK'
Welcome to openssl wiki

Generating a File Hash[edit]

One of the most basic uses of the dgst command (short for digest) is viewing the hash of a given file. To do this, simply invoke the command with the specified digest algorithm to use. For this example, I will be hashing an arbitrary file on my system using the MD5, SHA1, and SHA384 algorithms.

$ openssl dgst -md5 primes.dat
MD5(primes.dat)= 7710839bb87d2c4c15a86c2b2c805664

$ openssl dgst -sha1 primes.dat
SHA1(primes.dat)= 5dfab70ce825591689f4a3f65910870a9022cd32

$ openssl dgst -sha384 primes.dat
SHA384(primes.dat)= 41399bdffe6850f5a44852d967f3db415654f20dc2eb6cd231772f6ea411876d85d44091ebbc6b1f4ce8673e64617271

For a list of the available digest algorithms, you can use the following command.

$ openssl list -digest-algorithms
RSA-MD4 => MD4
RSA-MD5 => MD5
RSA-MDC2 => MDC2
RSA-RIPEMD160 => RIPEMD160
RSA-SHA1 => SHA1
RSA-SHA1-2 => RSA-SHA1
...

You can also use a similar command to see the available digest commands:

$ openssl list -digest-commands
blake2b512        blake2s256        gost              md4               
md5               mdc2              rmd160            sha1              
sha224            sha256            sha3-224          sha3-256          
sha3-384          sha3-512          sha384            sha512            
sha512-224        sha512-256        shake128          shake256          
sm3      

Below are three sample invocations of the md5, sha1, and sha384 digest commands using the same file as the dgst command invocation above.

$ openssl md5 primes.dat
MD5(primes.dat)= 7710839bb87d2c4c15a86c2b2c805664

$ openssl sha1 primes.dat
SHA1(primes.dat)= 5dfab70ce825591689f4a3f65910870a9022cd32

$ openssl sha384 primes.dat
SHA384(primes.dat)= 41399bdffe6850f5a44852d967f3db415654f20dc2eb6cd231772f6ea411876d85d44091ebbc6b1f4ce8673e64617271

File Encryption and Decryption[edit]

The following example demonstrates a simple file encryption and decryption using the enc command. The first argument is the cipher algorithm to use for encrypting the file. For this example I carefully selected the AES-256 algorithm in CBC Mode by looking up the available ciphers and picking out the first one I saw. To see the list of available ciphers, you can use the following command.

$ openssl enc -ciphers
Supported ciphers:
-aes-128-cbc               -aes-128-cfb               -aes-128-cfb1             
-aes-128-cfb8              -aes-128-ctr               -aes-128-ecb              
-aes-128-ofb               -aes-192-cbc               -aes-192-cfb              
-aes-192-cfb1              -aes-192-cfb8              -aes-192-ctr
...

You can also use the following command:

$ openssl list -cipher-algorithms
AES-128-CBC
AES-128-CBC-HMAC-SHA1
AES-128-CBC-HMAC-SHA256
id-aes128-CCM
AES-128-CFB
AES-128-CFB1
AES-128-CFB8
AES-128-CTR
...

Having selected an encryption algorithm, you must then specify whether the action you are taking is either encryption or decryption via the -e or -d flags, respectively. The -iter flag specifies the number of iterations on the password used for deriving the encryption key. A higher iteration count increases the time required to brute-force the resulting file. Using this option implies enabling use of the Password-Based Key Derivation Function 2, usually set using the -pbkdf2 flag. We then use the -salt flag to enable the use of a randomly generated salt in the key-derivation function.

Putting it all together, you can see the command to encrypt a file and the corresponding output below. Note that the passwords entered by the user are blank, just as they would usually be in a terminal session.

$ openssl enc -aes-256-cbc -e -iter 1000 -salt -in primes.dat -out primes.enc
enter aes-256-cbc encryption password:
Verifying - enter aes-256-cbc encryption password:

The analogous decryption command is as follows:

$ openssl enc -aes-256-cbc -d -iter 1000 -in primes.enc -out primes.dec
enter aes-256-cbc decryption password:

Commands[edit]

There are three different kinds of commands. These are standard commands, cipher commands, and digest commands. Calling the OpenSSL top-level help command with no arguments will result in openssl printing all available commands by group, sorted alphabetically.

Standard Commands[edit]

Overview of OpenSSL's command line utilities
Command Description
asn1parse Parse an ASN.1 sequence.
ca Certificate Authority (CA) Management.
ciphers Cipher Suite Description Determination.
cms CMS (Cryptographic Message Syntax) utility.
crl Certificate Revocation List (CRL) Management.
crl2pkcs7 CRL to PKCS#7 Conversion.
dgst Message Digest calculation. MAC calculations are superseded by mac(1).
dhparam Generation and Management of Diffie-Hellman Parameters. Superseded by genpkey(1) and pkeyparam(1).
dsa DSA Data Management.
dsaparam DSA Parameter Generation and Management. Superseded by genpkey(1) and pkeyparam(1).
ec EC (Elliptic curve) key processing.
ecparam EC parameter manipulation and generation.
enc Encoding with Ciphers.
engine Engine (loadable module) information and manipulation.
errstr Error Number to Error String Conversion.
gendsa Generation of DSA Private Key from Parameters. Superseded by genpkey(1) and pkey(1).
genpkey Generation of Private Key or Parameters.
genrsa Generation of RSA Private Key. Superseded by genpkey(1).
info Display diverse information built into the OpenSSL libraries.
kdf Key Derivation Functions.
mac Message Authentication Code Calculation.
nseq Create or examine a Netscape certificate sequence.
ocsp Online Certificate Status Protocol utility.
passwd Generation of hashed passwords.
pkcs12 PKCS#12 Data Management.
pkcs7 PKCS#7 Data Management.
pkcs8 PKCS#8 format private key conversion tool.
pkey Public and private key management.
pkeyparam Public key algorithm parameter management.
pkeyutl Public key algorithm cryptographic operation utility.
prime Compute prime numbers.
rand Generate pseudo-random bytes.
rehash Create symbolic links to certificate and CRL files named by the hash values.
req PKCS#10 X.509 Certificate Signing Request (CSR) Management.
rsa RSA key management.
rsautl RSA utility for signing, verification, encryption, and decryption. Superseded by pkeyutl(1).
s_client This implements a generic SSL/TLS client which can establish a transparent connection to a remote server speaking SSL/TLS.
s_server This implements a generic SSL/TLS server which accepts connections from remote clients speaking SSL/TLS.
s_time SSL Connection Timer.
sess_id SSL Session Data Management.
smime S/MIME mail processing.
speed Algorithm Speed Measurement.
spkac SPKAC printing and generating utility.
srp Maintain SRP password file.
storeutl Utility to list and display certificates, keys, CRLs, etc.
ts Time Stamping Authority tool (client/server).
verify X.509 Certificate Verification.
version OpenSSL Version Information.
x509 X.509 Certificate Data Management.

Further reading[edit]

  • Paul Heinlein. "OpenSSL Command-Line HOWTO". Has many quick cookbook-style recipes for doing common tasks using the "oppenssl" command-line application.