106 lines
3.6 KiB
Plaintext
106 lines
3.6 KiB
Plaintext
<DRAFT!>
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HOWTO keys
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1. Introduction
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Keys are the basis of public key algorithms and PKI. Keys usually
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come in pairs, with one half being the public key and the other half
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being the private key. With OpenSSL, the private key contains the
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public key information as well, so a public key doesn't need to be
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generated separately.
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Public keys come in several flavors, using different cryptographic
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algorithms. The most popular ones associated with certificates are
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RSA and DSA, and this HOWTO will show how to generate each of them.
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2. To generate a RSA key
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A RSA key can be used both for encryption and for signing.
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Generating a key for the RSA algorithm is quite easy, all you have to
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do is the following:
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openssl genrsa -des3 -out privkey.pem 2048
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With this variant, you will be prompted for a protecting password. If
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you don't want your key to be protected by a password, remove the flag
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'-des3' from the command line above.
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The number 2048 is the size of the key, in bits. Today, 2048 or
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higher is recommended for RSA keys, as fewer amount of bits is
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consider insecure or to be insecure pretty soon.
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3. To generate a DSA key
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A DSA key can be used for signing only. It is important to
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know what a certificate request with a DSA key can really be used for.
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Generating a key for the DSA algorithm is a two-step process. First,
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you have to generate parameters from which to generate the key:
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openssl dsaparam -out dsaparam.pem 2048
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The number 2048 is the size of the key, in bits. Today, 2048 or
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higher is recommended for DSA keys, as fewer amount of bits is
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consider insecure or to be insecure pretty soon.
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When that is done, you can generate a key using the parameters in
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question (actually, several keys can be generated from the same
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parameters):
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openssl gendsa -des3 -out privkey.pem dsaparam.pem
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With this variant, you will be prompted for a protecting password. If
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you don't want your key to be protected by a password, remove the flag
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'-des3' from the command line above.
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4. To generate an EC key
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An EC key can be used both for key agreement (ECDH) and signing (ECDSA).
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Generating a key for ECC is similar to generating a DSA key. These are
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two-step processes. First, you have to get the EC parameters from which
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the key will be generated:
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openssl ecparam -name prime256v1 -out prime256v1.pem
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The prime256v1, or NIST P-256, which stands for 'X9.62/SECG curve over
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a 256-bit prime field', is the name of an elliptic curve which generates the
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parameters. You can use the following command to list all supported curves:
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openssl ecparam -list_curves
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When that is done, you can generate a key using the created parameters (several
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keys can be produced from the same parameters):
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openssl genpkey -des3 -paramfile prime256v1.pem -out private.key
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With this variant, you will be prompted for a password to protect your key.
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If you don't want your key to be protected by a password, remove the flag
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'-des3' from the command line above.
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You can also directly generate the key in one step:
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openssl ecparam -genkey -name prime256v1 -out private.key
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or
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openssl genpkey -algorithm EC -pkeyopt ec_paramgen_curve:P-256
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5. NOTE
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If you intend to use the key together with a server certificate,
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it may be reasonable to avoid protecting it with a password, since
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otherwise someone would have to type in the password every time the
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server needs to access the key.
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For X25519 and X448, it's treated as a distinct algorithm but not as one of
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the curves listed with 'ecparam -list_curves' option. You can use
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the following command to generate an X25519 key:
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openssl genpkey -algorithm X25519 -out xkey.pem
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