# CFSSL

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## CloudFlare's PKI/TLS toolkit

CFSSL is CloudFlare's PKI/TLS swiss army knife. It is both a command line
tool and an HTTP API server for signing, verifying, and bundling TLS
certificates. It requires Go 1.16+ to build.

Note that certain linux distributions have certain algorithms removed
(RHEL-based distributions in particular), so the golang from the
official repositories will not work. Users of these distributions should
[install go manually](//golang.org/dl) to install CFSSL.

CFSSL consists of:

* a set of packages useful for building custom TLS PKI tools
* the `cfssl` program, which is the canonical command line utility
  using the CFSSL packages.
* the `multirootca` program, which is a certificate authority server
  that can use multiple signing keys.
* the `mkbundle` program is used to build certificate pool bundles.
* the `cfssljson` program, which takes the JSON output from the
  `cfssl` and `multirootca` programs and writes certificates, keys,
  CSRs, and bundles to disk.

### Building

Building cfssl requires a
[working Go 1.16+ installation](http://golang.org/doc/install).

```
$ git clone git@github.com:cloudflare/cfssl.git
$ cd cfssl
$ make
```

The resulting binaries will be in the bin folder:
```
$ tree bin
bin
├── cfssl
├── cfssl-bundle
├── cfssl-certinfo
├── cfssl-newkey
├── cfssl-scan
├── cfssljson
├── mkbundle
└── multirootca

0 directories, 8 files
```

#### Cross Compilation

You can set the `GOOS` and `GOARCH` environment variables to have Go cross compile for alternative platforms; however, cfssl requires cgo, and cgo requires a working compiler toolchain for the target platform.

### Installation

Installation requires a [working Go 1.16+ installation](http://golang.org/doc/install).
Alternatively, [prebuilt binaries are available](https://github.com/cloudflare/cfssl/releases)

```
$ go get github.com/cloudflare/cfssl/cmd/cfssl
```

will download, build, and install the CFSSL tool.

To install any of the other utility programs that are
in this repo (for instance `cfssljson` in this case):

```
$ go get github.com/cloudflare/cfssl/cmd/cfssljson
```

This will download, build, and install the CFSSLJSON tool.

And to simply install __all__ of the programs in this repo:

```
$ go get github.com/cloudflare/cfssl/cmd/...
```

if you are above go 1.18:

```
$ go install github.com/cloudflare/cfssl/cmd/...@latest
```

This will download, build, and install all of the utility programs
(including `cfssl`, `cfssljson`, and `mkbundle` among others).

### Using the Command Line Tool

The `cfssl` command line tool takes a command to specify what
operation it should carry out:

       sign             signs a certificate
       bundle           build a certificate bundle
       genkey           generate a private key and a certificate request
       gencert          generate a private key and a certificate
       serve            start the API server
       version          prints out the current version
       selfsign         generates a self-signed certificate
       print-defaults   print default configurations

Use `cfssl [command] -help` to find out more about a command.
The `version` command takes no arguments.

#### Signing

```
cfssl sign [-ca cert] [-ca-key key] [-hostname comma,separated,hostnames] csr [subject]
```

The `csr` is the client's certificate request. The `-ca` and `-ca-key`
flags are the CA's certificate and private key, respectively. By
default, they are `ca.pem` and `ca_key.pem`. The `-hostname` is
a comma separated hostname list that overrides the DNS names and
IP address in the certificate SAN extension.
For example, assuming the CA's private key is in
`/etc/ssl/private/cfssl_key.pem` and the CA's certificate is in
`/etc/ssl/certs/cfssl.pem`, to sign the `cloudflare.pem` certificate
for cloudflare.com:

```
cfssl sign -ca     /etc/ssl/certs/cfssl.pem       \
           -ca-key /etc/ssl/private/cfssl_key.pem \
           -hostname cloudflare.com               \
           ./cloudflare.pem
```

It is also possible to specify CSR with the `-csr` flag. By doing so,
flag values take precedence and will overwrite the argument.

The subject is an optional file that contains subject information that
should be used in place of the information from the CSR. It should be
a JSON file as follows:

```json
{
    "CN": "example.com",
    "names": [
        {
            "C":  "US",
            "L":  "San Francisco",
            "O":  "Internet Widgets, Inc.",
            "OU": "WWW",
            "ST": "California"
        }
    ]
}
```

**N.B.** As of Go 1.7, self-signed certificates will not include
[the AKI](https://go.googlesource.com/go/+/b623b71509b2d24df915d5bc68602e1c6edf38ca).

#### Bundling

```
cfssl bundle [-ca-bundle bundle] [-int-bundle bundle] \
             [-metadata metadata_file] [-flavor bundle_flavor] \
             -cert certificate_file [-key key_file]
```

The bundles are used for the root and intermediate certificate
pools. In addition, platform metadata is specified through `-metadata`.
The bundle files, metadata file (and auxiliary files) can be
found at:

        https://github.com/cloudflare/cfssl_trust

Specify PEM-encoded client certificate and key through `-cert` and
`-key` respectively. If key is specified, the bundle will be built
and verified with the key. Otherwise the bundle will be built
without a private key. Instead of file path, use `-` for reading
certificate PEM from stdin. It is also acceptable that the certificate
file should contain a (partial) certificate bundle.

Specify bundling flavor through `-flavor`. There are three flavors:
`optimal` to generate a bundle of shortest chain and most advanced
cryptographic algorithms, `ubiquitous` to generate a bundle of most
widely acceptance across different browsers and OS platforms, and
`force` to find an acceptable bundle which is identical to the
content of the input certificate file.

Alternatively, the client certificate can be pulled directly from
a domain. It is also possible to connect to the remote address
through `-ip`.

```
cfssl bundle [-ca-bundle bundle] [-int-bundle bundle] \
             [-metadata metadata_file] [-flavor bundle_flavor] \
             -domain domain_name [-ip ip_address]
```

The bundle output form should follow the example:

```json
{
    "bundle": "CERT_BUNDLE_IN_PEM",
    "crt": "LEAF_CERT_IN_PEM",
    "crl_support": true,
    "expires": "2015-12-31T23:59:59Z",
    "hostnames": ["example.com"],
    "issuer": "ISSUER CERT SUBJECT",
    "key": "KEY_IN_PEM",
    "key_size": 2048,
    "key_type": "2048-bit RSA",
    "ocsp": ["http://ocsp.example-ca.com"],
    "ocsp_support": true,
    "root": "ROOT_CA_CERT_IN_PEM",
    "signature": "SHA1WithRSA",
    "subject": "LEAF CERT SUBJECT",
    "status": {
        "rebundled": false,
        "expiring_SKIs": [],
        "untrusted_root_stores": [],
        "messages": [],
        "code": 0
    }
}
```


#### Generating certificate signing request and private key

```
cfssl genkey csr.json
```

To generate a private key and corresponding certificate request, specify
the key request as a JSON file. This file should follow the form:

```json
{
    "hosts": [
        "example.com",
        "www.example.com",
        "https://www.example.com",
        "jdoe@example.com",
        "127.0.0.1"
    ],
    "key": {
        "algo": "rsa",
        "size": 2048
    },
    "names": [
        {
            "C":  "US",
            "L":  "San Francisco",
            "O":  "Internet Widgets, Inc.",
            "OU": "WWW",
            "ST": "California"
        }
    ]
}
```

#### Generating self-signed root CA certificate and private key

```
cfssl genkey -initca csr.json | cfssljson -bare ca
```

To generate a self-signed root CA certificate, specify the key request as
a JSON file in the same format as in 'genkey'. Three PEM-encoded entities
will appear in the output: the private key, the csr, and the self-signed
certificate.

#### Generating a remote-issued certificate and private key.

```
cfssl gencert -remote=remote_server [-hostname=comma,separated,hostnames] csr.json
```

This calls `genkey` but has a remote CFSSL server sign and issue
the certificate. You may use `-hostname` to override certificate SANs.

#### Generating a local-issued certificate and private key.

```
cfssl gencert -ca cert -ca-key key [-hostname=comma,separated,hostnames] csr.json
```

This generates and issues a certificate and private key from a local CA
via a JSON request. You may use `-hostname` to override certificate SANs.


#### Updating an OCSP responses file with a newly issued certificate

```
cfssl ocspsign -ca cert -responder key -responder-key key -cert cert \
 | cfssljson -bare -stdout >> responses
```

This will generate an OCSP response for the `cert` and add it to the
`responses` file. You can then pass `responses` to `ocspserve` to start an
OCSP server.

### Starting the API Server

CFSSL comes with an HTTP-based API server; the endpoints are
documented in [`doc/api/intro.txt`](doc/api/intro.txt). The server is started with the `serve`
command:

```
cfssl serve [-address address] [-ca cert] [-ca-bundle bundle] \
            [-ca-key key] [-int-bundle bundle] [-int-dir dir] [-port port] \
            [-metadata file] [-remote remote_host] [-config config] \
            [-responder cert] [-responder-key key] [-db-config db-config]
```

Address and port default to "127.0.0.1:8888". The `-ca` and `-ca-key`
arguments should be the PEM-encoded certificate and private key to use
for signing; by default, they are `ca.pem` and `ca_key.pem`. The
`-ca-bundle` and `-int-bundle` should be the certificate bundles used
for the root and intermediate certificate pools, respectively. These
default to `ca-bundle.crt` and `int-bundle.crt` respectively. If the
`-remote` option is specified, all signature operations will be forwarded
to the remote CFSSL.

`-int-dir` specifies an intermediates directory. `-metadata` is a file for
root certificate presence. The content of the file is a json dictionary 
(k,v) such that each key k is an SHA-1 digest of a root certificate while value v 
is a list of key store filenames. `-config` specifies a path to a configuration
file. `-responder` and  `-responder-key` are the certificate and the
private key for the OCSP responder, respectively.

The amount of logging can be controlled with the `-loglevel` option. This
comes *after* the serve command:

```
cfssl serve -loglevel 2
```

The levels are:

* 0 - DEBUG
* 1 - INFO (this is the default level)
* 2 - WARNING
* 3 - ERROR
* 4 - CRITICAL

### The multirootca

The `cfssl` program can act as an online certificate authority, but it
only uses a single key. If multiple signing keys are needed, the
`multirootca` program can be used. It only provides the `sign`,
`authsign` and `info` endpoints. The documentation contains instructions
for configuring and running the CA.

### The mkbundle Utility

`mkbundle` is used to build the root and intermediate bundles used in
verifying certificates. It can be installed with

```
go get github.com/cloudflare/cfssl/cmd/mkbundle
```

It takes a collection of certificates, checks for CRL revocation (OCSP
support is planned for the next release) and expired certificates, and
bundles them into one file. It takes directories of certificates and
certificate files (which may contain multiple certificates). For example,
if the directory `intermediates` contains a number of intermediate
certificates:

```
mkbundle -f int-bundle.crt intermediates
```

will check those certificates and combine valid certificates into a single
`int-bundle.crt` file.

The `-f` flag specifies an output name; `-loglevel` specifies the verbosity
of the logging (using the same loglevels as above), and `-nw` controls the
number of revocation-checking workers.

### The cfssljson Utility

Most of the output from `cfssl` is in JSON. The `cfssljson` utility can take
this output and split it out into separate `key`, `certificate`, `CSR`, and
`bundle` files as appropriate. The tool takes a single flag, `-f`, that
specifies the input file, and an argument that specifies the base name for
the files produced. If the input filename is `-` (which is the default),
cfssljson reads from standard input. It maps keys in the JSON file to
filenames in the following way:

* if __cert__ or __certificate__ is specified,         __basename.pem__          will be produced.
* if __key__  or __private_key__ is specified,         __basename-key.pem__      will be produced.
* if __csr__  or __certificate_request__ is specified, __basename.csr__          will be produced.
* if __bundle__       is specified,                    __basename-bundle.pem__   will be produced.
* if __ocspResponse__ is specified,                    __basename-response.der__ will be produced.

Instead of saving to a file, you can pass `-stdout` to output the encoded
contents to standard output.

### Static Builds

By default, the web assets are accessed from disk, based on their
relative locations. If you wish to distribute a single,
statically-linked, `cfssl` binary, you’ll want to embed these resources
before building. This can by done with the
[go.rice](https://github.com/GeertJohan/go.rice) tool.

```
pushd cli/serve && rice embed-go && popd
```

Then building with `go build` will use the embedded resources.

### Additional Documentation

Additional documentation can be found in the "doc" directory:

* [doc/api/intro.txt](doc/api/intro.txt): documents the API endpoints
