HOWTO keys

HOWTO keys

1. Introduction

Keys are the basis of public key algorithms and PKI.  Keys usually

come in pairs, with one half being the public key and the other half

being the private key.  With OpenSSL, the private key contains the

public key information as well, so a public key doesn't need to be

generated separately.

Public keys come in several flavors, using different cryptographic

algorithms.  The most popular ones associated with certificates are

RSA and DSA, and this HOWTO will show how to generate each of them.

2. To generate a RSA key

A RSA key can be used both for encryption and for signing.

Generating a key for the RSA algorithm is quite easy, all you have to

do is the following:

  openssl genrsa -des3 -out privkey.pem 2048

With this variant, you will be prompted for a protecting password.  If

you don't want your key to be protected by a password, remove the flag

'-des3' from the command line above.

    NOTE: if you intend to use the key together with a server

    certificate, it may be a good thing to avoid protecting it

    with a password, since that would mean someone would have to

    type in the password every time the server needs to access

    the key.

The number 2048 is the size of the key, in bits.  Today, 2048 or

higher is recommended for RSA keys, as fewer amount of bits is

consider insecure or to be insecure pretty soon.

3. To generate a DSA key

A DSA key can be used for signing only.  This is important to keep

in mind to know what kind of purposes a certificate request with a

DSA key can really be used for.

Generating a key for the DSA algorithm is a two-step process.  First,

you have to generate parameters from which to generate the key:

  openssl dsaparam -out dsaparam.pem 2048

The number 2048 is the size of the key, in bits.  Today, 2048 or

higher is recommended for DSA keys, as fewer amount of bits is

consider insecure or to be insecure pretty soon.

When that is done, you can generate a key using the parameters in

question (actually, several keys can be generated from the same

parameters):

  openssl gendsa -des3 -out privkey.pem dsaparam.pem

With this variant, you will be prompted for a protecting password.  If

you don't want your key to be protected by a password, remove the flag

'-des3' from the command line above.

    NOTE: if you intend to use the key together with a server

    certificate, it may be a good thing to avoid protecting it

    with a password, since that would mean someone would have to

    type in the password every time the server needs to access

    the key.

-- 

Richard Levitte