Generate Fingerprint From Public Key Online

12.04.2020

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Generate Fingerprint From Private Key
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Public Key Definition

How to Generate a Public/Private KeyPair for Use With Solaris Secure Shell

Generate fingerprint from public key online banking

Users must generate a public/private key pair when their site implementshost-based authentication or user public-key authentication. For additionaloptions, see the ssh-keygen(1) manpage.

Jun 03, 2013 How to know public key fingerprint 5 years back,one of my U.S system admin was very security conscious.He asked me to create idrsa.pub key in server. I created the key with ssh-keygen -t rsa command.And send it him through encrypted email. Next day he wrote me,what is the ssh key fingerprint? Get fingerprint hashes of Base64 keys. Ssh-keyscan prints the host key of the SSH server in Base64-encoded format. To convert this to a fingerprint hash, the ssh-keygen utility can be used with its -l option to print the fingerprint of the specified public key. If using Bash, Zsh (or the Korn shell), process substitution can be used for a handy. The fingerprint is 20 bytes instead of 16 for MD5 used in the older package format. For V4 it is required to extract the public key packet first. This is likely to be the most tricky part, as PGP uses it's own packet format. You'll have to parse the binary data within your base 64 encoded blob to find the packet.

Before You Begin

Determine from your system administrator if host-based authenticationis configured.

Online RSA key generation: RSA (Rivest, Shamir and Adleman) is an asymmetric (or public-key) cryptosystem which is often used in combination with a symmetric cryptosystem such as AES (Advanced Encryption Standard).
The -l option instructs to show the fingerprint in the public key while the -f option specifies the file of the key to list the fingerprint for. To generate the missing public key again from the private key, the following command will generate the public key of the private key provided with the -f.
In order to provide a public key, each user in your system must generate one if they don’t already have one. This process is similar across all operating systems. First, you should check to make sure you don’t already have a key. By default, a user’s SSH keys are stored in that user’s /.ssh directory.
The fingerprint is a short version of the server's public key; it is easier for you to verify than the full key. It is very hard to spoof another public key with the same fingerprint. When you connect to a machine for the first time you do not have the fingerprint in your knownhosts, so ssh has nothing to compare it to, so it asks you.

Start the key generation program.

where -t is the type of algorithm, one of rsa, dsa, or rsa1.
Specify the path to the file that will hold the key.
Bydefault, the file name id_rsa, which represents an RSAv2 key, appears in parentheses. You can select this file by pressing the Return key. Or, you can type an alternative file name.

The file name of the public key is created automatically by appendingthe string .pub to the name of the private key file.
Type a passphrase for using your key.
This passphraseis used for encrypting your private key. A null entry is stronglydiscouraged. Note that the passphrase is not displayed when youtype it in.
Retype the passphrase to confirm it.
Check the results.
Check that the path to the keyfile is correct.

At this point, you have created a public/private key pair.
Choose the appropriate option:
- If your administrator has configuredhost-based authentication, you might need to copy the local host's publickey to the remote host.
  You can now log in to the remote host.For details, see How to Log In to a Remote Host With Solaris Secure Shell.
  1. Type the command on one line with no backslash.
  2. When you are prompted, supply your login password.
- If your site uses user authentication with public keys, populateyour authorized_keys file on the remote host.
  1. Copy your public key to the remote host.
    Type thecommand on one line with no backslash.
  2. When you are prompted, supply your login password.
    Whenthe file is copied, the message “Key copied” is displayed.
(Optional) Reduce the prompting for passphrases.
For a procedure, see How to Reduce Password Prompts in Solaris Secure Shell. For more information, see the ssh-agent(1) and ssh-add(1) man pages.

Example 19–2 Establishing a v1 RSA Key for a User

In the following example, the user cancontact hosts that run v1 of the Solaris Secure Shell protocol. To be authenticated by v1hosts, the user creates a v1 key, then copies the public key portion to theremote host.

In public-key cryptography, a public key fingerprint is a short sequence of bytes used to identify a longer public key. Fingerprints are created by applying a cryptographic hash function to a public key. Since fingerprints are shorter than the keys they refer to, they can be used to simplify certain key management tasks. In Microsoft software, 'thumbprint' is used instead of 'fingerprint'.

Creating public key fingerprints[edit]

A public key fingerprint is typically created through the following steps:

A public key (and optionally some additional data) is encoded into a sequence of bytes. To ensure that the same fingerprint can be recreated later, the encoding must be deterministic, and any additional data must be exchanged and stored alongside the public key. The additional data is typically information which anyone using the public key should be aware of. Examples of additional data include: which protocol versions the key should be used with (in the case of PGP fingerprints); and the name of the key holder (in the case of X.509 trust anchor fingerprints, where the additional data consists of an X.509 self-signed certificate).
The data produced in the previous step is hashed with a cryptographic hash function such as SHA-1 or SHA-2.
If desired, the hash function output can be truncated to provide a shorter, more convenient fingerprint.

This process produces a short fingerprint which can be used to authenticate a much larger public key. For example, whereas a typical RSA public key will be 1024 bits in length or longer, typical MD5 or SHA-1 fingerprints are only 128 or 160 bits in length.

When displayed for human inspection, fingerprints are usually encoded into hexadecimal strings. These strings are then formatted into groups of characters for readability. For example, a 128-bit MD5 fingerprint for SSH would be displayed as follows:

Using public key fingerprints for key authentication[edit]

When a public key is received over an untrusted channel, such as the Internet, the recipient often wishes to authenticate the public key. Fingerprints can help accomplish this, since their small size allows them to be passed over trusted channels where public keys won't easily fit.

For example, if Alice wishes to authenticate a public key as belonging to Bob, she can contact Bob over the phone or in person and ask him to read his fingerprint to her, or give her a scrap of paper with the fingerprint written down. Alice can then check that this trusted fingerprint matches the fingerprint of the public key. Exchanging and comparing values like this is much easier if the values are short fingerprints instead of long public keys.

Fingerprints can also be useful when automating the exchange or storage of key authentication data. For example, if key authentication data needs to be transmitted through a protocol or stored in a database where the size of a full public key is a problem, then exchanging or storing fingerprints may be a more viable solution.

In addition, fingerprints can be queried with search engines in order to ensure that the public key that a user just downloaded can be seen by third party search engines. If the search engine returns hits referencing the fingerprint linked to the proper site(s), one can feel more confident that the key is not being injected by an attacker, such as a Man-in-the-middle attack.

PGP developed the PGP word list to facilitate the exchange of public key fingerprints over voice channels.

Public key fingerprints in practice[edit]

In systems such as SSH, users can exchange and check fingerprints manually to perform key authentication. Once a user has accepted another user's fingerprint, that fingerprint (or the key it refers to) will be stored locally along with a record of the other user's name or address, so that future communications with that user can be automatically authenticated.

In systems such as X.509-based PKI, fingerprints are primarily used to authenticate root keys. These root keys issue certificates which can be used to authenticate user keys. This use of certificates eliminates the need for manual fingerprint verification between users.

In systems such as PGP or Groove, fingerprints can be used for either of the above approaches: they can be used to authenticate keys belonging to other users, or keys belonging to certificate-issuing authorities. In PGP, normal users can issue certificates to each other, forming a web of trust, and fingerprints are often used to assist in this process (e.g., at key-signing parties).

In systems such as CGA or SFS and most cryptographic peer-to-peer networks, fingerprints are embedded into pre-existing address and name formats (such as IPv6 addresses, file names or other identification strings). If addresses and names are already being exchanged through trusted channels, this approach allows fingerprints to piggyback on them.^[1]

Generate Fingerprint From Private Key

In PGP, most keys are created in such a way so that what is called the 'key ID' is equal to the lower 32 or 64 bits respectively of a key fingerprint. PGP uses key IDs to refer to public keys for a variety of purposes. These are not, properly speaking, fingerprints, since their short length prevents them from being able to securely authenticate a public key. Generating private key and ssl signed certificate free. 32bit key ids should not be used as current hardware can generate 32bit key id in just 4 seconds.^[2]

Security of public key fingerprints[edit]

The primary threat to the security of a fingerprint is a preimage attack, where an attacker constructs a key pair whose public key hashes to a fingerprint that matches the victim's fingerprint. The attacker could then present his public key in place of the victim's public key to masquerade as the victim.

A secondary threat to some systems is a collision attack, where an attacker constructs multiple key pairs which hash to his own fingerprint. This may allow an attacker to repudiate signatures he has created, or cause other confusion.

To prevent preimage attacks, the cryptographic hash function used for a fingerprint should possess the property of second preimage resistance. If collision attacks are a threat, the hash function should also possess the property of collision-resistance. While it is acceptable to truncate hash function output for the sake of shorter, more usable fingerprints, the truncated fingerprints must be long enough to preserve the relevant properties of the hash function against brute-force search attacks.

In practice, most fingerprints commonly used today are based on non-truncated MD5 or SHA-1 hashes. As of 2017, collisions but not preimages can be found in MD5 and SHA-1. The future is therefore likely to bring increasing use of newer hash functions such as SHA-256. However, fingerprints based on SHA-256 and other hash functions with long output lengths are more likely to be truncated than (relatively short) MD5 or SHA-1 fingerprints.

In situations where fingerprint length must be minimized at all costs, the fingerprint security can be boosted by increasing the cost of calculating the fingerprint. For example, in the context of Cryptographically Generated Addresses, this is called 'Hash Extension' and requires anyone calculating a fingerprint to search for a hashsum starting with a fixed number of zeroes^[3], which is assumed to be an expensive operation.