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Table of Contents

Generating a new keypair

Exchanging keys

Encrypting and decrypting documents

Making and verifying signatures

Apr 04, 2017  To encrypt your communication, the first thing to do is to create a new keypair. GPG is able to create several types of keypairs, but a primary key must be capable of making signatures. # gpg -gen-key Please select what kind of key you want: Your selection? 1 RSA keys may be between 1024 and 4096 bits long. What keysize do you want? Sometimes there is a need to generate random passwords or phrases automatically. We also offer an entirely browser-based secure online password/passphrase generator. Protecting a Private Key. The purpose of the passphrase is usually to encrypt the private key. This makes the key file by itself useless to.

GnuPG is a tool for secure communication.This chapter is a quick-start guide that covers the core functionalityof GnuPG.This includes keypair creation, exchanging and verifying keys, encryptingand decrypting documents, and authenticating documents with digitalsignatures.It does not explain in detail the concepts behind public-key cryptography,encryption, and digital signatures.This is covered in Chapter 2.It also does not explain how to use GnuPG wisely.This is covered in Chapters 3 and 4.

GnuPG uses public-key cryptography so that users may communicate securely.In a public-key system, each user has a pair of keys consisting ofa private key and a public key.A user's private key is kept secret; it need never be revealed.The public key may be given to anyone with whom the user wants tocommunicate.GnuPG uses a somewhat more sophisticated scheme in which a user hasa primary keypair and then zero or more additional subordinate keypairs.The primary and subordinate keypairs are bundled to facilitate keymanagement and the bundle can often be considered simply as one keypair.

The command-line option --gen-keyis used to create a new primary keypair.GnuPG is able to create several different types of keypairs, but a primarykey must be capable of making signatures.There are therefore only three options.Option 1 actually creates two keypairs.A DSA keypair is the primary keypair usable only for making signatures.An ElGamal subordinate keypair is also created for encryption. Option 2 is similar but creates only a DSA keypair.Option 4[1] creates a single ElGamal keypair usable for both making signatures and performing encryption.In all cases it is possible to later add additional subkeys for encryptionand signing.For most users the default option is fine.

You must also choose a key size.The size of a DSA key must be between 512 and 1024 bits, and an ElGamalkey may be of any size.GnuPG, however, requires that keys be no smaller than 768 bits.Therefore, if Option 1 was chosen and you choose a keysize larger than1024 bits, the ElGamal key will have the requested size, but the DSAkey will be 1024 bits.The longer the key the more secure it is against brute-force attacks,but for almost all purposes the default keysize is adequate sinceit would be cheaper to circumvent the encryption than try to break it.Also, encryption and decryption will be slower as thekey size is increased, and a larger keysize may affect signature length.Once selected, the keysize can never be changed.

Finally, you must choose an expiration date.If Option 1 was chosen, the expiration date will be used for both theElGamal and DSA keypairs.For most users a key that does not expire is adequate.The expiration time should be chosen with care, however,since although it is possible to change the expiration date after the keyis created, it may be difficult to communicate a changeto users who have your public key.

You must provide a user ID in addition to the key parameters.The user ID is used to associate the key being created with a realperson.Only one user ID is created when a key is created, but it is possibleto create additional user IDs if you want to use the key in two ormore contexts, e.g., as an employee at work and a political activiston the side.A user ID should be created carefully since it cannot be edited afterit is created. Particle illusion free download full version for mac.

GnuPG needs a passphrase to protect the primary and subordinate private keys that you keep in your possession.There is no limit on the length of a passphrase, and it should becarefully chosen.From the perspective of security, the passphrase to unlock the privatekey is one of the weakest points in GnuPG (and other public-key encryption systems as well) since it is the only protection you have if another individual gets your private key.Ideally, the passphrase should not use words from a dictionary andshould mix the case of alphabetic characters as well as use non-alphabetic characters.A good passphrase is crucial to the secure use of GnuPG.

Generating a revocation certificate

After your keypair is created you should immediately generate a revocationcertificate for the primary public key using the option--gen-revoke.If you forget your passphrase or if your private key is compromised or lost, this revocation certificate may be published to notify othersthat the public key should no longer be used.A revoked public key can still be used to verify signatures madeby you in the past, but it cannot be used to encrypt future messagesto you.It also does not affect your ability to decrypt messages sent toyou in the past if you still do have access to the private key.The argument mykey must be a keyspecifier,either the key ID of your primary keypair or any part of a user IDthat identifies your keypair.The generated certificate will be left in the filerevoke.asc.If the --output option is omitted, the result will be placed on standard output.Since the certificate is short, you may wish to print a hardcopy ofthe certificate to store somewhere safe such as your safe deposit box.The certificate should not be stored where others can access it sinceanybody can publish the revocation certificate and render thecorresponding public key useless.

Notes

[1]

Option 3 is to generate an ElGamal keypair that isnot usable for making signatures.

I know how to cange a passphrase for openssh using ssh-keygen command. How do I change a GPG encryption key’s passphrase on Linux or Unix like operating systems? How do I change the passphrase of the secret key using gpg?
gpg is the OpenPGP part of the GNU Privacy Guard (GnuPG). It is a tool to provide digital encryption and signing services using the OpenPGP standard. You can use the gpg command for complete key management including setting up keys, change key passphrase, list keys and much more.

Change the passphrase of the secret key

The syntax is:
gpg --edit-key Your-Key-ID-Here
gpg>passwd
gpg>save
You need type the passwd command followed by the save command at gpg> prompt to change the passphrase for your key-ID.

Examples

First, list your keys with the following command:

Gpg Passphrase File

Sample outputs:

You need to note down the public key 9AABBCD8. Next, type the following command:

Sample outputs:

Type the passwd command at gpg> prompt to change the passphrase:

You need to supply old passphrase to unlock the secret key:

Finally, enter the new passphrase:

To save all changes to the key rings and quit, type save at gpg> prompt:

Gpg Export Key With Passphrase

For more information read gpg(1) man page.

Generate Key Code

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