Public And Private Key Examples
Java Public Private

If a code signer does not yet have a suitable private key for signing the code, the key must first be generated, along with a corresponding public key that can be used by the code receiver's runtime system to verify the signature.

The command generates a public/private key pair for the entity whose distinguished name has a common name of Susan Jones and the organizational unit of Purchasing. The command creates a self-signed certificate that includes the public key and the distinguished-name information. You can generate Certificate in java dynamically, by using a pair or keys. (Public Key, Private Keys). Get These keys as BigInteger format and checking the following code to generate certificate.

Since this lesson assumes that you don't yet have such keys, you are going to create a keystore named examplestore and create an entry with a newly generated public/private key pair (with the public key in a certificate).

Public And Private Key Examples

Type the following command in your command window to create a keystore named examplestore and to generate keys:

You will be prompted to enter passwords for the key and keystore.

Subparts of the keytool Command

Let's look at what each of the keytool subparts mean.

Java Public Private

The command for generating keys is -genkey.
The -alias signFiles subpart indicates the alias to be used in the future to refer to the keystore entry containing the keys that will be generated.
The -keystore examplestore subpart indicates the name (and optionally path) of the keystore you are creating or already using.
The storepass value that you are promted for specifies the keystore password.
The keypass value that you are prompted for specifies a password for the private key about to be generated. You will always need this password in order to access the keystore entry containing that key. The entry doesn't have to have its own password. When you are prompted for the key password, you are given the option of letting it be the same as the keystore password.

Note: For security reasons you should not set your key or keystore passwords on the command line, because they can be intercepted more easily that way.

Distinguished-Name Information

If you use the preceding keystore command, you will be prompted for your distinguished-name information. Following are the prompts; the bold indicates what you should type.

Command Results

The keytool command creates the keystore named examplestore (if it doesn't already exist) in the same directory in which the command is executed. The command generates a public/private key pair for the entity whose distinguished name has a common name of Susan Jones and the organizational unit of Purchasing.

The command creates a self-signed certificate that includes the public key and the distinguished-name information. (The distinguished name you supply will be used as the 'subject' field in the certificate.) This certificate will be valid for 90 days, the default validity period if you don't specify a -validity option. The certificate is associated with the private key in a keystore entry referred to by the alias signFiles.

Self-signed certificates are useful for developing and testing an application. However, users are warned that the application is signed with an untrusted certificate and asked if they want to run the application. To provide users with more confidence to run your application, use a certificate issued by a recognized certificate authority.

Note: The command could be shorter if option defaults are accepted or you wish to be prompted for various values. Whenever you execute a keytool command, defaults are used for unspecified options that have default values, and you are prompted for any required values. For the genkey command, options with default values include alias (whose default is mykey), validity (90 days), and keystore (the file named .keystore in your home directory). Required values include dname, storepass, and keypass.

The KeyPairGenerator class is used to generate pairs of public and private keys. Key pair generators are constructed using the getInstance factory methods (static methods that return instances of a given class). Public

A Key pair generator for a particular algorithm creates a public/private key pair that can be used with this algorithm. It also associates algorithm-specific parameters with each of the generated keys.

There are two ways to generate a key pair: in an algorithm-independent manner, and in an algorithm-specific manner. The only difference between the two is the initialization of the object:

Algorithm-Independent Initialization
All key pair generators share the concepts of a keysize and a source of randomness. The keysize is interpreted differently for different algorithms (e.g., in the case of the DSA algorithm, the keysize corresponds to the length of the modulus). There is an initialize method in this KeyPairGenerator class that takes these two universally shared types of arguments. There is also one that takes just a keysize argument, and uses the SecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation of SecureRandom, a system-provided source of randomness is used.)
Since no other parameters are specified when you call the above algorithm-independent initialize methods, it is up to the provider what to do about the algorithm-specific parameters (if any) to be associated with each of the keys.
If the algorithm is the DSA algorithm, and the keysize (modulus size) is 512, 768, or 1024, then the Sun provider uses a set of precomputed values for the p, q, and g parameters. If the modulus size is not one of the above values, the Sun provider creates a new set of parameters. Other providers might have precomputed parameter sets for more than just the three modulus sizes mentioned above. Still others might not have a list of precomputed parameters at all and instead always create new parameter sets.
Algorithm-Specific Initialization
For situations where a set of algorithm-specific parameters already exists (e.g., so-called community parameters in DSA), there are two initialize methods that have an AlgorithmParameterSpec argument. One also has a SecureRandom argument, while the the other uses the SecureRandom implementation of the highest-priority installed provider as the source of randomness. (If none of the installed providers supply an implementation of SecureRandom, a system-provided source of randomness is used.)

In case the client does not explicitly initialize the KeyPairGenerator (via a call to an initialize method), each provider must supply (and document) a default initialization. For example, the Sun provider uses a default modulus size (keysize) of 1024 bits.

Note that this class is abstract and extends from KeyPairGeneratorSpi for historical reasons. Application developers should only take notice of the methods defined in this KeyPairGenerator class; all the methods in the superclass are intended for cryptographic service providers who wish to supply their own implementations of key pair generators.

Every implementation of the Java platform is required to support the following standard KeyPairGenerator algorithms and keysizes in parentheses:

DiffieHellman (1024)
DSA (1024)
RSA (1024, 2048)

These algorithms are described in the KeyPairGenerator section of the Java Cryptography Architecture Standard Algorithm Name Documentation. Consult the release documentation for your implementation to see if any other algorithms are supported.

Generate Public And Private Key Java