Questions tagged [ssh]
The Secure Socket Shell (SSH) protocol is an authentication protocol (described in RFC 4252) for securely getting access to a remote computer.
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SSH Server Configuration Best Practices? [migrated]
I hope this is the right place to post this.
I have been tasked with reviewing the settings of an SSH server, I'm currently trying to figure out what are the best practices, and I'm having a bit of ...
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Coursera Course or book(s) That covers the following subjects: OPENSSL, SSH, PKI, MD5, RSA, Certificates, keys, signatures
I started working as a developper in a cryptography company 3 months ago where the applications are for mostly windows applications. I found that I don't have enough knowledge concerning the topics ...
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Where are the seeds for the initial key exchange phase taken from?
I know that the standard DH and ECDH key exchange algorithms require the client and server to agree on a large prime number and a generator (in the DH algorithm) or a curve and a point (in the ECDH ...
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265 views
Is it possible to unscramble a scrambled ed25519 SSH key?
Let's say I generate an ed25519 SSH key with ssh-keygen -t ed25519. Then I take the private key file and randomly scramble the order of base64 encoded characters. ...
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Why if i change some characters of a Public key on authorizedKeys the login still works
This question is similar to:
[1]
Why does my SSH private key still work after changing some bytes in the file?
But in this case (on Windows) after editing the authorized_keys file and changing some ...
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SSH - Diffie-Hellman; prime & g exchange [duplicate]
The Diffie-Hellman key exchange algorithm can be used with SSH.
But how does SSH exchange the large safe prime p and the ...
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75 views
How to generate private SSH RSA key from given primes?
I have two primes and public exponent. How I can generate private key with this values and "ssh-rsa" format?
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Question about SSH host key algorithms
I'm currently writing a report for my Master's degree on the SSH protocol. Quite interesting!
However I'm having trouble getting into the inner workings of the host key algorithms.
For example, ...
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Why OpenSSH prefers ECDSA nistp256 keys over -384 and -521, and those over Ed25519, for host key verification?
According to ssh_config(5), HostKeyAlgorithms “specifies the host key algorithms that the client wants to use in order of ...
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1answer
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How exactly is signature verification done in SSH v2 authentication?
One of the authentication methods in SSH involves the client signing a message with its private key and sending it to the server for verification.
RFC 4252 (page 9) says:
...
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1answer
147 views
Prior art: SSH key authn over TLS?
I’m developing an application that runs over TLS. In addition to password-based authentication we’d like to be able to use SSH keys.
Is there any prior art in using SSH keys for authentication over ...
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Can a duplicate ssh private key be dangerous?
For convenience I had an id_rsa keypair and duplicated them with a new name. I may or may not use them consistently on different machines. (The reason was to keep an existing id_rsa on a machine I ...
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What's the downside of using X.509 in SSH instead of PKI
ssh uses public keys for authentication and not signed X.509 certificates. Specify a drawback which would be the use of X.509 certificates instead of public keys.
I've tried to look up a lot of ...
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where are ssh.com's crypticore and seed defined?
ssh.com's Tectia offers a few algorithms seemingly unique to itself. Chief among them: crypticore128@ssh.com, crypticore-mac@ssh.com and seed-cbc@ssh.com
Are these algorithms publicly defined ...
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Why does SSH authentication protocol send a challenge message instead of using digital signature to verify client
Why does SSH authentication protocol choose to have the server with the public key send a challenge message encrypted with this public key of the client instead of having the client send a message ...
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1answer
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Is there asymmetric encryption in SSH?
I've read in DigitalOcean article about SSH that in order for a server to authenticate a client:
The server sends the client this encrypted message.
If the client actually has the associated ...
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1answer
737 views
Is SSH over TLS 1.2/1.3 overkill?
I am designing a protocol that will have security in mind as one of its key goals. Currently I have selected SSH with TLS as the underlying transport.
I selected SSH because it had a variety of ...
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236 views
How the counter of AES-CTR in SSH is used
I am currently trying to decrypt an SSH session using memory derived keys and IVs.
My current problem is that the counter value seems to be the IV plus some value < 256.
My question is now why the ...
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2answers
838 views
How does the SSH server know the length of data encrypted?
In am learning the SSH RFC
An encryption algorithm and a key will be negotiated during the key
exchange. When encryption is in effect, the packet length, padding
length, payload, and padding fields ...
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3answers
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Is the curve25519 algorithm a special(implementation) one of ECDH?
It's the first time for me to learn about Key Exchange Protocol. And I thought that in both ECDH and DH there is a necessary step to share some public infomation(the common parameters) to each sides ...
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1answer
65 views
Book request about elliptic curves, RSA and DSA
I understand that this question can be hardly downvoted, but so be it if someone gives me really useful references :)
I wanna learn difference (deeply) between RSA, DSA, and ECC, especially I am ...
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1answer
67 views
Is there any point to encrypting a file if it's transferred via ssh?
Suppose I have two machines which can ssh into each other. Is there very little point in using gpg with a password protected symmetric cipher to transfer a ...
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how does AES GCM in SSH work?
I was looking at RFC5647: AES Galois Counter Mode for the Secure Shell Transport Layer Protocol and had some questions about section 7.1 "IV and Counter Management". Here's that section:
<...
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Sharing RSA private key between SSH and SSL services. How bad is it?
An appliance uses a curious way of obtaining ssh-rsa host keys: There is a single configuration option "management certificate" that sets RSA private keys both for HTTPS and SSH management.
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1answer
559 views
Are SSH key-pairs an example of a zero knowledge proof?
Quoting from source, authentication using SSH key pairs goes something like this:
1) The client begins by sending an ID for the key pair it would like
to authenticate with to the server.
2) ...
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3answers
256 views
How is public-key cryptography secure?
Quite strange question, but here goes:
I don't quite understand how asymmetric encryption works. Take SSH for an example: The server will always be listening for commands, so anyone who has the ...
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1answer
799 views
What is the encoding protocol for passphrase protected RSA private keys?
What is the protocol used to encode an RSA key protected with a passphrase?
If I generate an RSA key with
ssh-keygen -t rsa -b 4096
and do:
...
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1answer
256 views
Reason for 3 rounds ChaCha in ChaCha20Poly1305@openssh
OpenSSH uses a slightly different ChaCha20Poly1305 AEAD construct then the one proposed by A. Langley and others for TLS.
The TLS version
The openSSH version (and here)
The openSSH version uses two ...
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1answer
261 views
Does it make sense to have long SSH Key with shorter Passphrase?
If we encrypt our data with a longer SSH key which is protected by a shorter passphrase (with a decent entropy), then the limiting factor is entropy of the passphrase. So why do we use a longer key at ...
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2answers
471 views
Max size for exponent and modulus in RSA and for y, p, q, g in DSS
I'm writing a method in Java to read SSH public key in RFC 4253 format, which, in my case, can be either RSA, or DSS.
What I really need is to read exponent and <...
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2answers
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Why doesn't SSH use TLS?
Most cryptographically protected protocols use TLS these days. This applies to mail protocols, HTTP and many others. The newly designed QUIC has also adopted TLS as its cryptography layer.
However, ...
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1answer
168 views
SSH sequence number validity?
Looking at RFC4253, I came across the notion that the MAC is applied the encoded packet concatenated with a sequence number which acts as a counter.
However, I couldn't find any information on how ...
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how does OpenSSH use bcrypt to set IV's?
I generated an encrypted OpenSSH private key for test purposes:
...
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1answer
417 views
Why hash ( clear text + Secret ) instead of hash (encrpt(clear text) [ + secret ] )
Here is an excellent article on how SSH Authentication and Encryption works.
While thinking about how MAC's work, I had the same doubt as one of the comments left on the post:
The client combines ...
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1answer
253 views
How does authentication work for SSH login with a public key?
For SSH public key authentication in Cisco IOS it is sufficient to add RSA public key hash instead of content of that public key.
For example:
...
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See the RSA's $n = p q, e \text{ and } d$ from ssh-keygen
For learning purposes, how to get the RSA's parameters (I use standard notation):
$n = p q $, where $p$ and $q$ are prime and $e$, $d$, such that $ed = 1 \ (mod\ \varphi (n)) $ when doing
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790 views
Public key cryptography instead of passwords for web authentication
The usual way for a user to authenticate themselves to a website at the application layer is with a shared secret - the user's password. If a user is connecting to a bank, they give the bank their ...
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Security implications of storing an ssh passphrase
I'm trying to understand the security implications of encrypting an ssh key with a passphrase, and storing the passphrase in the MacOS key chain or Gnome key-ring.
As I understand it, my ssh key ...
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2answers
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ed25519 ssh public key is always 80 characters long?
I am creating some ssh keys using ed25519, something like:
...
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1answer
1k views
Is encrypt-and-MAC secure for AES-CTR + UMAC?
OpenSSH will (especially in older versions) use AES-CTR plus a MAC in encrypt-and-MAC. This is not secure in general (meaning that there exist secure ciphers and secure MACs such that using them in ...
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Can I use a GnuPG created key for OpenSSH or authentication purposes? [closed]
I created a key pair using PGP (GnuPG) for the purpose of encrypting and signing data (documents, emails, and so on). That key was created with the RSA algorithm, and naturally starts with:
-----...
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3answers
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How many KDF rounds for an SSH key?
What is the best practice on choosing how many key derivation function (KDF) rounds/iterations when generating an SSH key pair with ssh-keygen?
Am I correct in saying that it is unnecessary if the ...
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3answers
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Which hash function is used for signatures ssh-rsa and ssh-dss?
I'm building a fuse client for ssh/sftp. I write the required ssh and sftp functions myself. Now I read in RFC4253 that before signing the data to sign is default hashed. In RFC4253 8. "Diffie-...
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Why public host key still need be sent in SSH_MSG_KEX_DH_GEX_REPLY?
RFC 4251(https://www.rfc-editor.org/rfc/rfc4251) states,
[page 4]
The protocol provides the option that the server name - host key
association is not checked when connecting to the host for the first
...
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1answer
787 views
server_host_key_algorithms in SSH
RFC 4253 "The Secure Shell (SSH) Transport Layer Protocol" states on page 18:
...
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Why SSH does not use a certificate authority in the same way as SSL [closed]
SSL requires the use of a trusted third party -- the certificate authority to verify a public key presented by a server to a client.
SSH on the other hand relies on the client having the server's ...
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Can a server's ECDSA fingerprint be spoofed during SSH?
I have read somewhere that Servers which have SSH access for users in the public can have their public key posted publicly (e.g., on a website), so that people who access such a server using SSH can ...
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1answer
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Why ssh-gen makes difference between PEM and PKCS8?
Correct me if I am wrong, but PKCS8 is format to store private key info. It could be binary-enoded (DER) or Base64 encoded (<...
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How does TLS differ from SSH from a strictly cryptographic perspective?
How does TLS differ from SSH from a strictly cryptographic perspective?
I know that there are many non-cryptographic differences between them, but I would like to know the cryptographic ones.
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1answer
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Why does my SSH private key still work after changing some bytes in the file?
I (for a test) just randomly altered a private RSA key by opening it up in Vim and changing a few bytes. It is the private part of an SSH key pair used for logging in on a remote system. Puzzlingly, ...
