OpenSSL: Difference between revisions
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Remember that variables may be expanded in assignments, much like how shell scripts work. For a more thorough explanation of the configuration file format, see {{man|5ssl|config}}. In some operating systems, this [[man page]] is named {{man|5|config|url=}} or {{man|5|openssl-config|url=}}. Sometimes, it may not even be available through the man hierarchy at all, for example, it may be placed in the following location {{ic|/usr/share/openssl}}. | Remember that variables may be expanded in assignments, much like how shell scripts work. For a more thorough explanation of the configuration file format, see {{man|5ssl|config}}. In some operating systems, this [[man page]] is named {{man|5|config|url=}} or {{man|5|openssl-config|url=}}. Sometimes, it may not even be available through the man hierarchy at all, for example, it may be placed in the following location {{ic|/usr/share/openssl}}. | ||
=== req section === | === req section === | ||
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string_mask= utf8only # Only allow utf8 strings in request/ca fields. | string_mask= utf8only # Only allow utf8 strings in request/ca fields. | ||
prompt= no # Do not prompt for field value confirmation. | prompt= no # Do not prompt for field value confirmation. | ||
}} | }} | ||
Revision as of 05:03, 6 July 2018
OpenSSL is an open-source implementation of the SSL and TLS protocols, dual-licensed under the OpenSSL (Apache License 1.0) and the SSLeay (4-clause BSD) licenses. It is supported on a variety of platforms, including BSD, Linux, OpenVMS, Solaris and Windows. It is designed to be as flexible as possible, and is free to use for both personal and commercial uses. It is based on the earlier SSLeay library. Version 1.0.0 of OpenSSL was released on March 29, 2010.
openssl is installed by default on Arch Linux.
SSL introduction
In order to focus on setting up a SSL/TLS solution, rather than explaining the bare basics regarding the subject, the approach used throughout the article to explain SSL concepts is by and large file-oriented.
Consult both Wikipedia:Certificate authority and Wikipedia:Public key infrastructure for more information.
- Certificate authority (CA)
- Certificate authorities return certificates from end-user requests. In order to do this, the returned end-user certificate is signed with the CA private key and CA certificate, which in turn contains the CA public key. CA also distribute certificate revocation lists (CRL) which tell the end-user what certificates are no longer valid, and when the next CRL is due.
- CA private key
- The CA private key is the crucial part of the trifecta. Exposing it would defeat the purpose of designating a central authority that validates and revokes permissions, and at the same time, it is the signed counter part to the CA public key used to certify against the CA certificate. An exposed CA private key could allow an attacker to replicate the CA certificate since the CA private key signature is embedded in the CA certificate itself.
- CA certificate and public key
- These are distributed in a single file to all end-users. They are used to certify other end-user certificates that claimed to be signed by the matching CA, such as mail servers or websites.
- End-users
- End-users submit certificate requests to the CA which contain a distinguished name (DN). Normally, CA do not allow more than one valid certificate with the same DN without revoking the previous one. End-user certificates may be revoked if they are not renewed when due, among other reasons.
- End-user generated key
- End-users generate keys in order to sign certificate requests that are submitted to the CA. As with the CA private key, an exposed user-key could facilitate impersonating the user to the point where an attacker could submit a request under the user's name, resulting in the CA revoking the former, legitimate, user certificate.
- Certificate requests
- These contain the user's DN and public key. As their name implies, they fully represent the initial part of the process of acquiring certification from a CA.
- End-user certificate
- The main distinction between an end-user certificate and CA certificate is that end-user ones cannot sign certificates themselves; they merely provide means of identification in exchanges of information.
- Certificate revocation list (CRL)
- CRLs are also signed with the CA key, but they only dictate information regarding end-user certificates. Usually, a 30 day span is given between new CRL submissions.
Configuration
The OpenSSL configuration file, conventionally placed in /etc/ssl/openssl.cnf
, may appear complicated at first. This section covers the essential settings.
Remember that variables may be expanded in assignments, much like how shell scripts work. For a more thorough explanation of the configuration file format, see config(5ssl). In some operating systems, this man page is named config(5) or openssl-config(5). Sometimes, it may not even be available through the man hierarchy at all, for example, it may be placed in the following location /usr/share/openssl
.
req section
Settings related to generating keys, requests and self-signed certificates.
The req section is responsible for the DN prompts. A general misconception is the Common Name (CN) prompt, which suggests that it should have the user's proper name as a value. End-user certificates need to have the machine hostname as CN, whereas CA should not have a valid TLD, so that there is no chance that, between the possible combinations of certified end-users' CN and the CA certificate's, there is a match that could be misinterpreted by some software as meaning that the end-user certificate is self-signed. Some CA certificates do not even have a CN, such as Equifax:
$ openssl x509 -subject -noout < /etc/ssl/certs/Equifax_Secure_CA.pem
subject= /C=US/O=Equifax/OU=Equifax Secure Certificate Authority
Even though splitting the files is not strictly necessary to normal functioning, it is very confusing to handle request generation and CA administration from the same configuration file, so it is advised to follow the convention of clearly separating the settings into two cnf
files and into two containing directories.
Here are the settings that are common to both tasks:
[ req ] # Default bit encryption and out file for generated keys. default_bits= 2048 default_keyfile=private/cakey.pem string_mask= utf8only # Only allow utf8 strings in request/ca fields. prompt= no # Do not prompt for field value confirmation.
End-user req settings
Makes a v3 request suitable for most circumstances:
distinguished_name=ca_dn # Distinguished name contents. req_extensions=req_v3 # For generating ca certificates. [ ca_dn ] C= US ST= New Jersey O= localdomain CN= localhost [ req_v3 ] basicConstraints= CA:FALSE keyUsage= nonRepudiation, digitalSignature, keyEncipherment
GOST engine support
First, be sure that libgost.so exist on your system
$ pacman -Ql openssl | grep libgost
In case everything is fine, add the following lines to the config:
openssl_conf = openssl_def # this must be a top-level declaration
Put the following lines in the end of the document:
[ openssl_def ] engines = engine_section [ engine_section ] gost = gost_section [ gost_section ] engine_id = gost soft_load = 1 dynamic_path = /usr/lib/engines/libgost.so default_algorithms = ALL CRYPT_PARAMS = id-Gost28147-89-CryptoPro-A-ParamSet
The official README.gost should contain more examples on this.
Generating keys
/etc/ssl/private/
directory like most other distributions do, see FS#43059.Before generating the key, make a secure directory to host it:
$ mkdir -m0700 private
Followed by preemptively assigning secure permissions for the key itself:
$ touch private/key.pem $ chmod 0600 private/key.pem
Alternatively set umask to restrict permissions of newly created files and directories:
$ umask 077
An example genpkey
key generation:
$ openssl genpkey -algorithm RSA -out private/key.pem -pkeyopt rsa_keygen_bits:4096
If an encrypted key is desired, use the following command. Password will be prompted for:
$ openssl genpkey -aes-256-cbc -algorithm RSA -out private/key.pem -pkeyopt rsa_keygen_bits:4096
Creating certificate signing requests
To obtain a certificate from a CA, whether a public one such as CAcert.org (ca-certificates-cacert) or a locally managed solution, a request file must be submitted which is known as a Certificate Signing Request or CSR.
Make a new request and sign it with a previously generated key:
$ openssl req -new -sha256 -key private/key.pem -out req.csr
Signing certificates
Covers the process of local CA signing: directly self-signed certificates or through a local CA.
Self-signed certificate
A significant amount of programs will not work with self-signed certificates, and maintaining more than one system with self-signed certificates is more trouble than investing the initial effort in setting up a certificate authority.
If a key was already generated as explained before, use this command to sign the new certificate with the aforementioned key:
$ openssl req -key private/key.pem -x509 -new -days 3650 -out selfcert.pem
If a key was not previously generated, to create a new private key and sign the certificate with this new key, use the following:
$ openssl req -nodes -newkey rsa:2048 -keyout newkey.pem -x509 -days 3650 -out selfcert.pem
Certificate authority
OpenSSL Certificate Authority is a detailed guide on using OpenSSL to act as a CA.
The method shown in this section is mostly meant to show how signing works; it is not suited for large deployments that need to automate signing a large number of certificates. Consider installing an SSL server for that purpose.
Before using the Makefile, make a configuration file according to #Configuration. Be sure to follow instructions relevant to CA administration; not request generation.
Makefile
Saving the file as Makefile
and issuing make
in the containing directory will generate the initial CRL along with its prerequisites:
OPENSSL= openssl CNF= openssl.cnf CA= ${OPENSSL} ca -config ${CNF} REQ= ${OPENSSL} req -config ${CNF} KEY= private/cakey.pem KEYMODE= RSA CACERT= cacert.pem CADAYS= 3650 CRL= crl.pem INDEX= index.txt SERIAL= serial CADEPS= ${CNF} ${KEY} ${CACERT} all: ${CRL} ${CRL}: ${CADEPS} ${CA} -gencrl -out ${CRL} ${CACERT}: ${CNF} ${KEY} ${REQ} -key ${KEY} -x509 -new -days ${CADAYS} -out ${CACERT} rm -f ${INDEX} touch ${INDEX} echo 100001 > ${SERIAL} ${KEY}: ${CNF} mkdir -m0700 -p $(dir ${KEY}) touch ${KEY} chmod 0600 ${KEY} ${OPENSSL} genpkey -algorithm ${KEYMODE} -out ${KEY} revoke: ${CADEPS} ${item} @test -n $${item:?'usage: ${MAKE} revoke item=cert.pem'} ${CA} -revoke ${item} ${MAKE} ${CRL} sign: ${CADEPS} ${item} @test -n $${item:?'usage: ${MAKE} sign item=request.csr'} mkdir -p newcerts ${CA} -in ${item} -out ${item:.csr=.crt}
To sign certificates:
$ make sign item=req.csr
To revoke certificates:
$ make revoke item=cert.pem
Troubleshooting
"bad decrypt" while decrypting
OpenSSL 1.1.0 changed the default digest algorithm for the dgst and enc commands from MD5 to SHA256. [1]
Therefore if a file has been encrypted using OpenSSL 1.0.2 or older, trying to decrypt it with an up to date version may result in an error like:
error:06065064:digital envelope routines:EVP_DecryptFinal_ex:bad decrypt:crypto/evp/evp_enc.c:540
Supplying the -md md5
option should solve the issue:
$ openssl enc -d -md md5 -in encrypted -out decrypted
See also
- Wikipedia page on OpenSSL, with background information.
- OpenSSL project page.
- FreeBSD Handbook
- Step-by-step guide to create a signed SSL certificate
- OpenSSL Certificate Authority
- Bulletproof SSL and TLS by Ivan Ristić, a more formal introduction to SSL/TLS