rsa - an old algorithm based on the difficulty of factoring large numbers. A key size of at least 2048 bits is recommended for RSA; 4096 bits is better. RSA is getting old and significant advances are being made in factoring. Choosing a different algorithm may be advisable. It is quite possible the RSA algorithm will become practically breakable in the foreseeable future. All SSH clients support this algorithm.
ssh keygen 4096 bit certificate
The host keys are usually automatically generated when an SSH server is installed. They can be regenerated at any time. However, if host keys are changed, clients may warn about changed keys. Changed keys are also reported when someone tries to perform a man-in-the-middle attack. Thus it is not advisable to train your users to blindly accept them. Changing the keys is thus either best done using an SSH key management tool that also changes them on clients, or using certificates.
OpenSSH does not support X.509 certificates. Tectia SSH does support them. X.509 certificates are widely used in larger organizations for making it easy to change host keys on a period basis while avoiding unnecessary warnings from clients. They also allow using strict host key checking, which means that the clients will outright refuse a connection if the host key has changed.
OpenSSH has its own proprietary certificate format, which can be used for signing host certificates or user certificates. For user authentication, the lack of highly secure certificate authorities combined with the inability to audit who can access a server by inspecting the server makes us recommend against using OpenSSH certificates for user authentication.
However, OpenSSH certificates can be very useful for server authentication and can achieve similar benefits as the standard X.509 certificates. However, they need their own infrastructure for certificate issuance.
Where do 4096 bit RSA keys for SSL certs currently stand in terms of things like CA support, browser support, etc? In the overall scheme of things is the increased security worth the risk of 4096 bit keys not having the widespread support and compatibility as 2048 bit keys do, not to mention the increased CPU load required to process the key exchange? Are things slowly turning in favor of 4096?
I always generate 4096 bit keys since the downside is minimal (slightly lower performance) and security is slightly higher (although not as high as one would like). Larger keys like 8192 bit or even larger take forever to generate and require specially patched sw to use so are impractical. Luckily there are other algorithms slowly replacing rsa...
Note: In this example, the 4096 parameter to the openssl genrsa command indicates that the generated key is 4096 bits long. A key that is 4096 bits or longer is considered more secure. A shorter key will be less secure, but will require less computation to use.
Note: Remember that this newly created certificate file should be used for test purposes only. Normally, you would need to create a certificate request and send it to a certificate authority (CA). The CA would then sign the certificate and give it back to you upon payment, thus providing you with authentication according to their outlined policies.
How it works [top]In order to enable HTTPS support for use with Iguana, you must first generate valid public key/private key certificates. These digital certificates are used to authenticate the sender. Keys are typically generated in pairs, with one being public and the other being private. The private key must be kept secret to ensure security. It is used to encrypt outgoing messages and decrypt incoming messages. A public key is the one that is released to the public. It allows anyone to use it for encrypting messages to be sent to the user, as well as for decrypting messages received from the user.
f you use OpenSSL to generate certificates, the private key will contain public key information, therefore the public key does not have to be generated separately. You will need to have OpenSSL installed on your machine. You can download OpenSSL for Windows or Linux from:
In addition to having a public/private key certificate, you must also obtain a certificate file from a certificate authority (CA), such as Verisign, which issues digital certificates for use by other parties. There are many commercial CAs that charge for their services, while other institutions may have their own CAs. To ensure that the web server (with HTTPS support enabled) functions as expected, you can create a self-signed certificate for use during the initial testing phase.
To create the keys, a preferred command is ssh-keygen, which is available with OpenSSH utilities in the Azure Cloud Shell, a macOS or Linux host, and Windows (10 & 11). ssh-keygen asks a series of questions and then writes a private key and a matching public key.
SSH keys are by default kept in the /.ssh directory. If you do not have a /.ssh directory, the ssh-keygen command creates it for you with the correct permissions. An SSH key is created as a resource and stored in Azure for later use.
The following ssh-keygen command generates 4096-bit SSH RSA public and private key files by default in the /.ssh directory. If an existing SSH key pair is found in the current location, those files are overwritten.
The key pair name for this article. Having a key pair named id_rsa is the default; some tools might expect the id_rsa private key file name, so having one is a good idea. The directory /.ssh/ is the default location for SSH key pairs and the SSH config file. If not specified with a full path, ssh-keygen creates the keys in the current working directory, not the default /.ssh.
Many people are taking a fresh look at IT security strategies in the wake of the NSA revelations. One of the issues that comes up is the need for stronger encryption, using public key cryptography instead of just passwords. This is sometimes referred to as certificate authentication, but certificates are just one of many ways to use public key technology.
One of the core decisions in this field is the key size. Most people have heard that 1024 bit RSA keys have been cracked and are not used any more for web sites or PGP. The next most fashionable number after 1024 appears to be 2048, but a lot of people have also been skipping that and moving to 4096 bit keys. This has lead to some confusion as people try to make decisions about which smartcards to use or which type of CA certificate to use. The discussion here is exclusively about RSA key pairs, although the concepts are similar for other algorithms (although key lengths are not equivalent)
Many types of public key cryptography, such as X.509, offer an expiry feature. This is not just a scheme to force you to go back to the certificate authority and pay more money every 12 months. It provides a kind of weak safety net in the case where somebody is secretly using an unauthorised copy of the key or a certificate that the CA issued to an imposter.
However, the expiry doesn't eliminate future algorithmic compromises. If, in the future, an attacker succeeds in finding a shortcut to break 2048 bit keys, then they would presumably crack the root certificate as easily as they crack the server certificates and then, using their shiny new root key, they would be in a position to issue new server certificates with extended expiry dates.
Therefore, the expiry feature alone doesn't protect against abuse of the key in the distant future. It does provide some value though: forcing people to renew certificates periodically allows the industry to bring in new minimum key length standards from time to time.
These developments may leave people feeling a little bit naked if they have to use a shorter 2048 bit key for any of the reasons suggested above (e.g. for wider choice of smart cards and compatibility with readers). It has also resulted in some people spending time looking for 4096 bit smart cards and compatible readers when they may be better off just using 2048 bits and investing their time in other security improvements.
In fact, the "risk" of using only 2048 rather than 4096 bits in the smartcard may well be far outweighed by the benefits of hardware security (especially if a smartcard reader with pin-pad is used)
My feeling is that the Debian preference for 4096 bit PGP keys is not based solely on security, rather, it is also influenced by the fact that Debian is a project run by volunteers. Given this background, there is a perception that if everybody migrates from 1024 to 2048, then there would be another big migration effort to move all users from 2048 to 4096 and that those two migrations could be combined into a single effort going directly from 1024 to 4096, reducing the future workload of the volunteers who maintain the keyrings. This is a completely rational decision for administrative reasons, but it is not a decision that questions the security of using 2048 bit keys today. Therefore, people should not see Debian's preference to use 4096 bit keys as a hint that 2048 bit keys are fundamentally flawed.
The GNFS complexity measurement is a heuristic: it's a tool to help you measure the relative strengths of different RSA key sizes but it is not exact. Implementation details, future vulnerabilities in RSA, and other factors can affect the strength of an RSA key. The attack that breaks RSA 2048 could also break RSA 4096.
Bigger RSA key sizes may slow down handshaking from the users point of view. On a Mac or Linux machine you can get some time taken to sign a 2048 bit RSA vs 4096 bit RSA with the openssl speed rsa command:
No. We can re-key pretty quickly, so deploying a 4096 bit key would be pretty easy, but we feel like a 2048 bit key provides a reasonable speed/security/compatibility tradeoff - as we might move to AWS in future, the last one is also a concern for us. 2ff7e9595c
Comments