Your public key has been saved in foo. Maarten Bodewes 1, 1 1 gold badge 9 9 silver badges 18 18 bronze badges. I found this answer helpful in the following scenario.
Your system uses SHA1 to calculate the fingerprint, but your friend's uses md5. This helped - thank you! This is the only answer that explains how the fingerprint is calculated — greuze. Bruno Bronosky Bruno Bronosky 1, 1 1 gold badge 16 16 silver badges 25 25 bronze badges. Mike Schroll Mike Schroll 3 3 bronze badges.
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Podcast Explaining the semiconductor shortage, and how it might end. Does ES6 make JavaScript frameworks obsolete? Featured on Meta. You can put the server keys fingerprint in DNS Domain Name System and get ssh to tell you if what it the two fingerprints match.
The above output should be used for bind versions earlier than 9. The complete record for the machine looks like: freshmint IN A You should see the SSHFP lines as above, although with old versions of host it may not display properly but like:. You can also specify this on the command line when connecting. Note how you are told how the DNS fingerprint matches:.
If the fingerprint in the DNS does not match you will see the following — you may have seen similar before, but this is on a first connection:. You don't really need to understand this bit to use the above; however if you are a technical nerd you will want to know. Foster auspost. Author: Alain D D Williams. You may not claim ownership or copyright of any substantially unmodified files.
Acknowledgement would be appreciated, but is not necessary. These demonstrations are made available in the hope that they are useful. There may be errors: there is no warranty at all, use at your own risk. Remember the courier with the locked briefcase handcuffed to his wrist? Public-key encryption puts him out of business probably to his relief. PGP then creates a session key, which is a one-time-only secret key. This key is a random number generated from the random movements of your mouse and the keystrokes you type.
This session key works with a very secure, fast conventional encryption algorithm to encrypt the plaintext; the result is ciphertext. Once the data is encrypted, the session key is then encrypted to the recipient's public key. This public key-encrypted session key is transmitted along with the ciphertext to the recipient. How PGP encryption works. Decryption works in the reverse. The recipient's copy of PGP uses his or her private key to recover the temporary session key, which PGP then uses to decrypt the conventionally-encrypted ciphertext.
How PGP decryption works. The combination of the two encryption methods combines the convenience of public key encryption with the speed of conventional encryption. Conventional encryption is about 1, times faster than public key encryption. Public key encryption in turn provides a solution to key distribution and data transmission issues. Used together, performance and key distribution are improved without any sacrifice in security.
However, public key size and conventional cryptography's secret key size are totally unrelated. A conventional bit key has the equivalent strength of a bit public key.
A conventional bit key is equivalent to a bit public key. Again, the bigger the key, the more secure, but the algorithms used for each type of cryptography are very different and thus comparison is like that of apples to oranges. While the public and private keys are mathematically related, it's very difficult to derive the private key given only the public key; however, deriving the private key is always possible given enough time and computing power.
This makes it very important to pick keys of the right size; large enough to be secure, but small enough to be applied fairly quickly. Additionally, you need to consider who might be trying to read your files, how determined they are, how much time they have, and what their resources might be.
Larger keys will be cryptographically secure for a longer period of time. If what you want to encrypt needs to be hidden for many years, you might want to use a very large key. Of course, who knows how long it will take to determine your key using tomorrow's faster, more efficient computers? There was a time when a bit symmetric key was considered extremely safe. Keys are stored in encrypted form. PGP stores the keys in two files on your hard disk; one for public keys and one for private keys.
These files are called keyrings. As you use PGP, you will typically add the public keys of your recipients to your public keyring. Your private keys are stored on your private keyring. If you lose your private keyring, you will be unable to decrypt any information encrypted to keys on that ring. A digital signature serves the same purpose as a handwritten signature. However, a handwritten signature is easy to counterfeit.
A digital signature is superior to a handwritten signature in that it is nearly impossible to counterfeit, plus it attests to the contents of the information as well as to the identity of the signer. Some people tend to use signatures more than they use encryption. The basic manner in which digital signatures are created is illustrated in Figure Instead of encrypting information using someone else's public key, you encrypt it with your private key.
If the information can be decrypted with your public key, then it must have originated with you. Simple digital signatures. PGP uses a cryptographically strong hash function on the plaintext the user is signing.
This generates a fixed-length data item known as a message digest. Again, any change to the information results in a totally different digest. Then PGP uses the digest and the private key to create the "signature. Upon receipt of the message, the recipient uses PGP to recompute the digest, thus verifying the signature. PGP can encrypt the plaintext or not; signing plaintext is useful if some of the recipients are not interested in or capable of verifying the signature. As long as a secure hash function is used, there is no way to take someone's signature from one document and attach it to another, or to alter a signed message in any way.
The slightest change in a signed document will cause the digital signature verification process to fail. Secure digital signatures.
Digital signatures play a major role in authenticating and validating other PGP users' keys. In a public key environment, it is vital that you are assured that the public key to which you are encrypting data is in fact the public key of the intended recipient and not a forgery. You could simply encrypt only to those keys which have been physically handed to you.
But suppose you need to exchange information with people you have never met; how can you tell that you have the correct key? Digital certificates, or certs, simplify the task of establishing whether a public key truly belongs to the purported owner. A certificate is a form of credential. Examples might be your driver's license, your social security card, or your birth certificate. Each of these has some information on it identifying you and some authorization stating that someone else has confirmed your identity.
Some certificates, such as your passport, are important enough confirmation of your identity that you would not want to lose them, lest someone use them to impersonate you. A digital certificate is data that functions much like a physical certificate. A digital certificate is information included with a person's public key that helps others verify that a key is genuine or valid.
Digital certificates are used to thwart attempts to substitute one person's key for another. A digital certificate consists of three things:.
Thus, a certificate is basically a public key with one or two forms of ID attached, plus a hearty stamp of approval from some other trusted individual. Anatomy of a PGP certificate. Certificate servers A certificate server, also calledacert server or a key server, is a database that allows users to submit and retrieve digital certificates.
A cert server usually provides some administrative features that enable a company to maintain its security policies — for example, allowing only those keys that meet certain requirements to be stored. Public Key Infrastructures A PKI contains the certificate storage facilities of a certificate server, but also provides certificate management facilities the ability to issue, revoke, store, retrieve, and trust certificates.
The main feature of a PKI is the introduction of what is known as a Certification Authority, orCA, whichisahumanentity — a person, group, department, company, or other association — that an organization has authorized to issue certificates to its computer users. A CA's role is analogous to a country's government's Passport Office.
A CA creates certificates and digitally signs them using the CA's private key. Using the CA's public key, anyone wanting to verify a certificate's authenticity verifies the issuing CA's digital signature, and hence, the integrity of the contents of the certificate most importantly, the public key and the identity of the certificate holder.
PGP recognizes two different certificate formats:. One unique aspect of the PGP certificate format is that a single certificate can contain multiple signatures. If you look on a public certificate server, you may notice that certain certificates, such as that of PGP's creator, Phil Zimmermann, contain many signatures. Some PGP certificates consist of a public key with several labels, each of which contains a different means of identifying the key's owner for example, the owner's name and corporate email account, the owner's nickname and home email account, a photograph of the owner — all in one certificate.
The list of signatures of each of those identities may differ; signatures attest to the authenticity that one of the labels belongs to the public key, not that all the labels on the key are authentic. Note that 'authentic' is in the eye of its beholder — signatures are opinions, and different people devote different levels of due diligence in checking authenticity before signing a key.
A PGP certificate. All X. In practice, however, different companies have created their own extensions to X. Acertificate requires someone to validate that a public key and the name of the key's owner go together. With PGP certificates, anyone can play the role of validator.
With X. Bear in mind that PGP certificates also fully support a hierarchical structure using a CA to validate certificates. The X. You might think of an X. It has your name and some information about you on it, plus the signature of the person who issued it to you.
Probably the most widely visible use of X. When you've assured yourself that a certificate belonging to someone else is valid, you can sign the copy on your keyring to attest to the fact that you've checked the certificate and that it's an authentic one.
If you want others to know that you gave the certificate your stamp of approval, you can export the signatureto a certificateserver so that others canseeit. As described in the section Public Key Infrastructures , some companies designate one or more Certification Authorities CAs to indicate certificate validity.
In an organization using a PKI with X. The fingerprint of a key is a unique sequence of letters and numbers used to identify the key. Just like the fingerprints of two different people, the fingerprints of two different keys can never be identical. The fingerprint is the best way to identify a particular key. A key has several properties like the name and email of the key owner, key type, key expiration date and so on.
When you are searching for a public key and you find multiple keys with the same properties, the only way to identify the key you are looking for is to compare the fingerprints of the two keys with the fingerprint of the key you require. It is the fingerprint of a key that is verified when you try to login to a remote computer using SSH.
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