Generate a static key: openvpn -genkey -secret static.key. Copy the static key to both client and server, over a pre-existing secure channel. Server configuration file dev tun ifconfig 10.8.0.1 10.8.0.2 secret static.key Client configuration file remote myremote.mydomain dev tun ifconfig 10.8.0.2 10.8.0.1 secret static.key Firewall configuration. Apr 03, 2020 A pre-shared key (also called a shared secret or PSK) is used to authenticate the Cloud VPN tunnel to your peer VPN gateway. As a security best practice, it's recommended that you generate a strong 32-character shared secret. Generated for you. To generate a private/public key pair from a pre-eixsting parameters file use the following: openssl ecparam -in secp256k1.pem -genkey -noout -out secp256k1-key.pem Or to do the equivalent operation without a parameters file use the following: openssl ecparam -name secp256k1 -genkey -noout -out secp256k1-key.pem. The communication between the server and clients should be encrypted with pre-shared keys. In my understanding, while a connection is established, the callbacks pskservercb and pskclientcb are called from the server side and client side respectively. These are the points to update the server and client pre-shared keys.
- Openssl Generate Pre Shared Key Mean
- Openssl Generate Pre Shared Key Mean
- Linksys Pre Shared Key
- Openssl Generate Pre Shared Key Generator
- Openssl Generate Pre Shared Key Found
Contents
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Parent page: Internet and Networking >> SSH
Public key authentication is more secure than password authentication. This is particularly important if the computer is visible on the internet. If you don't think it's important, try logging the login attempts you get for the next week. My computer - a perfectly ordinary desktop PC - had over 4,000 attempts to guess my password and almost 2,500 break-in attempts in the last week alone.
With public key authentication, the authenticating entity has a public key and a private key. Each key is a large number with special mathematical properties. The private key is kept on the computer you log in from, while the public key is stored on the .ssh/authorized_keys file on all the computers you want to log in to. When you log in to a computer, the SSH server uses the public key to 'lock' messages in a way that can only be 'unlocked' by your private key - this means that even the most resourceful attacker can't snoop on, or interfere with, your session. As an extra security measure, most SSH programs store the private key in a passphrase-protected format, so that if your computer is stolen or broken in to, you should have enough time to disable your old public key before they break the passphrase and start using your key. Wikipedia has a more detailed explanation of how keys work.
Public key authentication is a much better solution than passwords for most people. In fact, if you don't mind leaving a private key unprotected on your hard disk, you can even use keys to do secure automatic log-ins - as part of a network backup, for example. Different SSH programs generate public keys in different ways, but they all generate public keys in a similar format:
Key-based authentication is the most secure of several modes of authentication usable with OpenSSH, such as plain password and Kerberos tickets. Key-based authentication has several advantages over password authentication, for example the key values are significantly more difficult to brute-force, or guess than plain passwords, provided an ample key length. Other authentication methods are only used in very specific situations.
SSH can use either 'RSA' (Rivest-Shamir-Adleman) or 'DSA' ('Digital Signature Algorithm') keys. Both of these were considered state-of-the-art algorithms when SSH was invented, but DSA has come to be seen as less secure in recent years. RSA is the only recommended choice for new keys, so this guide uses 'RSA key' and 'SSH key' interchangeably.
Key-based authentication uses two keys, one 'public' key that anyone is allowed to see, and another 'private' key that only the owner is allowed to see. To securely communicate using key-based authentication, one needs to create a key pair, securely store the private key on the computer one wants to log in from, and store the public key on the computer one wants to log in to.
Using key based logins with ssh is generally considered more secure than using plain password logins. This section of the guide will explain the process of generating a set of public/private RSA keys, and using them for logging into your Ubuntu computer(s) via OpenSSH.
The first step involves creating a set of RSA keys for use in authentication.
This should be done on the client.
To create your public and private SSH keys on the command-line:
You will be prompted for a location to save the keys, and a passphrase for the keys. This passphrase will protect your private key while it's stored on the hard drive:
Your public key is now available as .ssh/id_rsa.pub in your home folder.
Congratulations! You now have a set of keys. Now it's time to make your systems allow you to login with them
Choosing a good passphrase
You need to change all your locks if your RSA key is stolen. Otherwise the thief could impersonate you wherever you authenticate with that key.
An SSH key passphrase is a secondary form of security that gives you a little time when your keys are stolen. If your RSA key has a strong passphrase, it might take your attacker a few hours to guess by brute force. That extra time should be enough to log in to any computers you have an account on, delete your old key from the .ssh/authorized_keys file, and add a new key.
Your SSH key passphrase is only used to protect your private key from thieves. It's never transmitted over the Internet, and the strength of your key has nothing to do with the strength of your passphrase.
The decision to protect your key with a passphrase involves convenience x security. Note that if you protect your key with a passphrase, then when you type the passphrase to unlock it, your local computer will generally leave the key unlocked for a time. So if you use the key multiple times without logging out of your local account in the meantime, you will probably only have to type the passphrase once.
If you do adopt a passphrase, pick a strong one and store it securely in a password manager. You may also write it down on a piece of paper and keep it in a secure place. If you choose not to protect the key with a passphrase, then just press the return when ssh-keygen asks.
Key Encryption Level
Note: The default is a 2048 bit key. You can increase this to 4096 bits with the -b flag (Increasing the bits makes it harder to crack the key by brute force methods).
Password Authentication
The main problem with public key authentication is that you need a secure way of getting the public key onto a computer before you can log in with it. If you will only ever use an SSH key to log in to your own computer from a few other computers (such as logging in to your PC from your laptop), you should copy your SSH keys over on a memory stick, and disable password authentication altogether. If you would like to log in from other computers from time to time (such as a friend's PC), make sure you have a strong password.
The key you need to transfer to the host is the public one. If you can log in to a computer over SSH using a password, you can transfer your RSA key by doing the following from your own computer:
Where <username> and <host> should be replaced by your username and the name of the computer you're transferring your key to.
Due to this bug, you cannot specify a port other than the standard port 22. You can work around this by issuing the command like this: ssh-copy-id '<username>@<host> -p <port_nr>'. If you are using the standard port 22, you can ignore this tip.
Another alternative is to copy the public key file to the server and concatenate it onto the authorized_keys file manually. It is wise to back that up first:
You can make sure this worked by doing:
You should be prompted for the passphrase for your key:
Enter passphrase for key '/home/<user>/.ssh/id_rsa': |
Enter your passphrase, and provided host is configured to allow key-based logins, you should then be logged in as usual.
Encrypted Home Directory
If you have an encrypted home directory, SSH cannot access your authorized_keys file because it is inside your encrypted home directory and won't be available until after you are authenticated. Therefore, SSH will default to password authentication.
To solve this, create a folder outside your home named /etc/ssh/<username> (replace '<username>' with your actual username). This directory should have 755 permissions and be owned by the user. Move the authorized_keys file into it. The authorized_keys file should have 644 permissions and be owned by the user.
Then edit your /etc/ssh/sshd_config and add:
Finally, restart ssh with:
The next time you connect with SSH you should not have to enter your password.
username@host's password:
If you are not prompted for the passphrase, and instead get just the
prompt as usual with password logins, then read on. There are a few things which could prevent this from working as easily as demonstrated above. On default Ubuntu installs however, the above examples should work. If not, then check the following condition, as it is the most frequent cause:
On the host computer, ensure that the /etc/ssh/sshd_config contains the following lines, and that they are uncommented;
If not, add them, or uncomment them, restart OpenSSH, and try logging in again. If you get the passphrase prompt now, then congratulations, you're logging in with a key!
Permission denied (publickey)
If you're sure you've correctly configured sshd_config, copied your ID, and have your private key in the .ssh directory, and still getting this error:
Permission denied (publickey). |
Chances are, your /home/<user> or ~/.ssh/authorized_keys permissions are too open by OpenSSH standards. You can get rid of this problem by issuing the following commands:
Error: Agent admitted failure to sign using the key.
This error occurs when the ssh-agent on the client is not yet managing the key. Issue the following commands to fix:
This command should be entered after you have copied your public key to the host computer.
Debugging and sorting out further problems
The permissions of files and folders is crucial to this working. You can get debugging information from both the client and server.
if you think you have set it up correctly , yet still get asked for the password, try starting the server with debugging output to the terminal.
To connect and send information to the client terminal
No matter how your public key was generated, you can add it to your Ubuntu system by opening the file .ssh/authorized_keys in your favourite text editor and adding the key to the bottom of the file. You can also limit the SSH features that the key can use, such as disallowing port-forwarding or only allowing a specific command to be run. This is done by adding 'options' before the SSH key, on the same line in the authorized_keys file. For example, if you maintain a CVS repository, you could add a line like this:
When the user with the specified key logged in, the server would automatically run /usr/bin/cvs server, ignoring any requests from the client to run another command such as a shell. For more information, see the sshd man page. /755
SSL stands for Secure Sockets Layer and was originally created by Netscape. SSLv2 and SSLv3 are the 2 versions of this protocol (SSLv1 was never publicly released). After SSLv3, SSL was renamed to TLS.
TLS stands for Transport Layer Security and started with TLSv1.0 which is an upgraded version of SSLv3.
Those protocols are standardized and described by RFCs.
OpenSSL provides an implementation for those protocols and is often used as the reference implementation for any new feature.
The goal of SSL was to provide secure communication using classical TCP sockets with very few changes in API usage of sockets to be able to leverage security on existing TCP socket code.
SSL/TLS is used in every browser worldwide to provide https ( http secure ) functionality.
The latest standard version is TLSv1.2 http://tools.ietf.org/html/rfc5246, while the upcoming TLS v1.3 is still in the draft stage.
Connection-less support is provided via DTLS.
Those protocols are configurable and can use various ciphers depending on their version.
- 1Security
- 1.2versions tricks
- 6TLS Extensions
- 7Server Authentication
- 8Client Authentication
- 9Alternate Authentication Methods
Security[edit]
Besides implementation problems leading to security issues, there is security inherent to the protocol itself.
It is recommended to run TLSv1.0, 1.1 or 1.2 and fully disable SSLv2 and SSLv3 that have protocol weaknesses.
For the very same reason it is recommended to control protocol downgrade.
POODLE : SSLv3 harmful[edit]
versions tricks[edit]
SCSV[edit]
Signaling cipher suite value (SCSV), i.e., it does not actually correspond to a suite of cryptosystems.Its presence is used to signal some facts or contextual information allowing it to not break existing implementations that just ignore this unsupported cipher suite.
SCSV was created with TLS_EMPTY_RENEGOTIATION_INFO_SCSV in rfc5746 draft. http://tools.ietf.org/html/rfc5746#section-3.3Usage of a cipher suite value is explained by the fact that some SSLv3 and TLSv1.0 implementations fail to ignore extensions that they do not support, so using a cipher suite allows the bypass of these implementation problems. Ssh key setup.
- TLS_EMPTY_RENEGOTIATION_INFO_SCSV 0x00 0xFF
openssl : SSL3_CK_SCSV
- TLS_FALLBACK_SCSV 0x56 0x00 See SSL MODE SEND FALLBACK SCSV
openssl : SSL3_CK_FALLBACK_SCSV
Handshake[edit]
A connection always starts with a handshake between a client and a server. This handshake is intended to provide a secret key to both client and server that will be used to cipher the flow.
In fact a master secret is obtained from the handshake from which the secret key is derived. In OpenSSL this master_secret is kept within the SSL Session SSL_SESSION.
The initial handshake can provide server authentication, client authentication or no authentication at all.
Default usage in HTTPS is to verify server authenticity with trusted Certificate Authorities known by the browser.
A quick presentation for a classical TLS handshake ( RSA, without Session tickets and without client authentication ) under CC BY license http://blog.artisanlogiciel.net/public/tech/classical_handshake.odp feel free to improve it.
Cipher Suites[edit]
- How are cipher suites negotiated?
What TLS 1.2 rfc says :
So basically server has the decision choice and does not provide a list of its own ciphersuites but just the selected one
What are best ciphersuites to choose ?
An interesting hint here: http://zombe.es/post/4078724716/openssl-cipher-selection
- Is there a normalized cipher suite ordering ?
Not much more than what is told for 'How cipher suites are negotiated?'
So it is implementation dependent. In openssl there are two modes:
- default is to choose the first compatible cipher suite from client hello.
- SSL_OP_CIPHER_SERVER_PREFERENCE to SSL_CTX_set_option to choose from server cipher list order.
- How to setup ciphersuites in openssl ?
Manual:SSL_CTX_set_cipher_list(3) where string cipher parameter is described in Manual:ciphers(1)
Session Resumption[edit]
Since the handshake uses public key cryptography heavily and this is CPU intensive compared to symmetric ( secret key ) cryptography, the protocol provides ways to reuse existing credentials to reissue new secret keys for new connections ( new TCP connections ) or to renew existing connections.
Browsers use this heavily when connecting to https sites since they open multiple connections to the same site at a time. The first connection does the handshake while all the others use a quick handshake (can be named resumed, abbreviated or restart handshake) allowing saving for both client and server CPU.
RFC 2246, section 7, p. 23
This explains difference the between an OpenSSL SSL Connection ( SSL ) and an SSL Session ( SSL_SESSION ) , each SSL Connection runs on its TCP connection and can share the same SSL Session with other SSL connections.
( to obtain session from connection use function : SSL_SESSION *SSL_get_session(const SSL *ssl) )
Renegotiation[edit]
On a Ssl connection a renegotiation can occur to request for new cipher suites or key materials.
To renegotiate :
a Client will send a ClientHello over its existing SSL connection
a Server will send a HelloRequest and expects Client to renegotiate with a ClientHello in very short time.
Server renegotiation ( without resumption ):
To use both renegotiation and resumption use : SSL_renegotiate_abbreviated(con) which won't request to recreate a new session ( since 1.0.1 ).
It created a vulnerability that was addressed by TLS extension to notify server whenever a connection is renegotiating and allows to verify it is legit.
This is RFC5746 'Transport Layer Security (TLS) Renegotiation Indication Extension' http://tools.ietf.org/html/rfc5746 to perform Secure Renegotiation
TLS Extensions[edit]
Server Name Indication[edit]
SNI Extension from RFC 3546, Transport Layer Security (TLS) Extensions.
Allows a client to specify at the very beginning of the handshake what server name it wants to connect to.
How to retrieve a private key on different server platforms: Using SSL/TLS Manager. On the cPanel home page, click on “SSL/TLS Manager” and then on the “Private keys” button. On the new screen, you. Using File manager. Click on the File manager button from the cPanel home screen and open the. Jul 09, 2019 The private key gets generated along with your Certificate Signing Request (CSR). The CSR is submitted to the certificate authority right after you activate your certificate, while the private key must be kept safe and secret on your server or device. Later on, this key is used for installation of your certificate. Jun 09, 2019 To do this, follow these steps: Log on to the computer that issued the certificate request by using an account that has administrative permissions. Click Start, click Run, type mmc, and then click OK. On the File menu, click. Add/Remove Snap-in. In the Add/Remove Snap-in dialog box, click Add. 
This is very useful for a web server that serves multiple domains but doesn't have a wildcard certificate or a certificate containing a full list of supported domains.
In this case the server can learn from the client what Certificate the client expects to receive.
See how a C program can use Libssl API and provide SNI information with SSL_set_tlsext_host_name See example in SSL/TLS_Client
Server Authentication[edit]
Server Certificate[edit]
This is Public Key Certified by a Certificate with Trust from the client. Trust from the client can be done automatically with Certificate Authority trust.
It is crucial that clients check the Server Certificate against the expected hostname Hostname_validation
No Authentication Aka Anonymous[edit]
Openssl Generate Pre Shared Key Mean
Even if it look like is a strange idea, it is possible to select cipher suite that does not provide any server authentication but still provide confidentiality.
Selecting string cipher aNULLManual:ciphers(1) allows to select such cipher suite. Remark this is not same a eNULL that provides no confidentiality at all.
Anonymous Diffie_Hellman exchange (DH) and Anonymous Elliptic Curves Diffie Hellman Exchange (ECDH) methods provide this anonymous authentication.
Client Authentication[edit]
Client authentication is optional. In many cases the client does not authenticate at the ssl layer, but rather with the usage of protocols above ssl, for example with HTTP authentication methods.
Openssl Generate Pre Shared Key Mean
Client Certificates[edit]
- Certificate Request ( TLS v1.2 http://tools.ietf.org/html/rfc5246#section-7.4.4 )
Server can send a Certificate Request with digest algorithms and a list CA Distinguished names which will be used by the client to select the Client Certificate it will send.
- Client Certificate ( TLS v1.2 http://tools.ietf.org/html/rfc5246#section-7.4.6)
Client send its Client Certificate first then all intermediate Certificates, if any, up to the CA ( optionally excluded ).
- CertificateVerify ( TLS v1.2 http://tools.ietf.org/html/rfc5246#section-7.4.8 )
The Client sends a Certificate Verify that is signed by the private key counterpart of its Client public key included in the Certificate with digest algorithm over whole handshake messages so far ( excluding this one of course ).
This proves that this client owns the private key that applies to this specific handshake and hence authenticates the client for this session.
Alternate Authentication Methods[edit]
Public Key Certificate[edit]
This is the most commonly used method. With X509 Certificates and Certficate Authorities.
It applies To Server Certificate or to Client Certificate authentication.
Depending on CipherSuite, for Server Public Key can be used to derive pre-master-key.
Pre-Shared Keys[edit]
TLS PSK Pre Shared Key
Kerberos[edit]
Password[edit]
TLS SRP : Secure Remote Password. Allows authentication with a password over TLS.
Supported by OpenSSL with version 1.0.1.
RFC5054
TLS SRP is negotiated with various ciphersuites, currently all use SHA to compute SRP.
Linksys Pre Shared Key
With SRP trust is based on the fact that both parties should know the password ( or Password Verifier ) to complete the SRP Verify Handshake.
Openssl Generate Pre Shared Key Generator
It is possible to use RSA or DSS additionaly to prove Server identity with Certificates.