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1. Diffie-hellman Dh Key How Long Generate Code
2. Diffie Hellman Generator
3. Diffie-hellman Dh Key How Long Generate Number
4. Diffie Hellman Key Exchange Example
5. Diffie-hellman Dh Key How Long Generate Pdf

I am trying to use the OpenSSL command line to generate a ECDH public key that meets the following specifications: Use a Base64 encoded X.509 SubjectPublicKeyInfo structure containing a ECDH pub.

Fixed Diffie-Hellman embeds the server's public parameter in the certificate, and the CA then signs the certificate. That is, the certificate contains the Diffie-Hellman public-key parameters, and those parameters never change. Ephemeral Diffie-Hellman uses temporary, public keys. Each instance or run of the protocol uses a different public key. Abstract: Many cryptographic applications are using bad groups for Diffie-Hellman-protocols: Either the prime is not a safe-prime or the generator doesn’t generate a prime-order-subgroup. The article explains the issues in detail and shows that they can cause terrible vulnerabilities. After that it provides a short guideline how to avoid the issues (use safe-primes and squares). For our webserver or VPN server, you want to use unique Diffie-Hellman parameters but you don’t know how to generate the.pem file using OpenSSL. Solution: Use this command to generate the parameters and save them in dhparams.pem: openssl dhparam -out dhparams.pem 4096. This command generates Diffie-Hellman parameters with 4096 bits. May 20, 2016 Diffie-Hellman works by calculating a shared secret based on our private key and the other party’s public key, so this is all we need in this case. The magic of DH is that each party will calculate the same value despite having different sets of keys available to them. Jan 28, 2019  Generate DH parameters by using the GUI. Navigate to Traffic Management SSL and, in the Tools group, select Create Diffie-Hellman (DH) key, and Configure SSL DH Param. Note: For information about DH parameters, see Diffe-Hellman (DH) parameters. Achieve perfect forward secrecy with DHE. Generating DH parameters is a CPU-intensive operation. To get a larger Ephemeral DH key length than 768 bits you need to be running on Java 8. 1024 is the new default, and you can go up to 2048 using the jdk.tls.ephemeralDHKeySize (details: customising DH keys). From what I could find, there is no concept of regenerating the key parameters separately in Java.

To use perfect forward secrecy cipher suites, you must set up Diffie-Hellman parameters (on the server side), or the PFS cipher suites will be silently ignored.

Diffie-Hellman[edit]

SSL_CTX_set_tmp_dh is used to set the Diffie-Hellman parameters for a context. One of the easiest ways to get Diffie-Hellman parameters to use with this function is to generate random Diffie-Hellman parameters with the dhparam command-line program with the -C option, and embed the resulting code fragment in your program. For example, openssl dhparam -C 2236 might result in:

Savethe private key file in a safe place. You'll need to provide the name of your keypairwhen you launch an instance and the corresponding private key each time you connectto theinstance.After you have created the key pair, use one of the following methods to import yourkey pair to Amazon EC2.New console. The namecan include up to 255 ASCII characters. To import the public key.Open the Amazon EC2 console at.In the navigation pane, choose Key Pairs.Choose Import key pair.For Name, enter a descriptive name for the key pair.

which can then be used like this:

Be sure to choose a bit length appropriate to the security level you want to achieve, although keep in mind that Diffie-Hellman parameters longer than 2236 bits may be incompatible with older versions of NSS. Even worse, it appears that versions of Java prior to 1.7 don't support Diffie-Hellman parameters longer than 1024 bits!

Validating Parameters[edit]

The Diffie-Hellman parameters should be validated after loading. To perform paramter validation, you call DH_check. DH_check returns 0 or a bitmask values of the following:

• DH_CHECK_P_NOT_PRIME (0x01)
• DH_CHECK_P_NOT_SAFE_PRIME (0x02)
• DH_UNABLE_TO_CHECK_GENERATOR (0x04)
• DH_NOT_SUITABLE_GENERATOR (0x08)

The validation code might look as follows (error checking omitted for clarity):

The additional call to BN_mod_word(dh->p, 24) (and unmasking of DH_NOT_SUITABLE_GENERATOR) is performed to ensure your program accepts IETF group parameters. OpenSSL checks the prime is congruent to 11 when g = 2; while the IETF's primes are congruent to 23 when g = 2. Without the test, the IETF parameters would fail validation. For details, see Diffie-Hellman Parameter Check (when g = 2, must p mod 24 11?).

Elliptic curve Diffie-Hellman[edit]

For elliptic curve Diffie-Hellman, you can do something like this:

Or, in OpenSSL 1.0.2 (not yet released, as of Feb 2013) and higher, you should be able to do:

For more information, see Elliptic Curve Diffie Hellman and Elliptic Curve Cryptography.

RFC 3526 PEM Encoded Groups[edit]

Below are three Diffie-Hellman MODP groups specified in RFC 3526, More Modular Exponential (MODP) Diffie-Hellman groups for Internet Key Exchange (IKE) (the 1024-bit parameter is from RFC 2409). They can be used with PEM_read_bio_DHparams and a memory BIO. RFC 3526 also offers 1536-bit, 6144-bit and 8192-bit primes.

Strong SSL Security on nginx

Published: 14-06-2015 Last update: 27-04-2019 Author: Remy van Elst Text only version of this article

Table of Contents

• The Cipher Suite

This tutorial shows you how to set up strong SSL security on the nginxwebserver. We do this by updating OpenSSL to the latest version to mitigateattacks like Heartbleed, disabling SSL Compression and EXPORT ciphers tomitigate attacks like FREAK, CRIME and LogJAM, disabling SSLv3 and below becauseof vulnerabilities in the protocol and we will set up a strong ciphersuite thatenables Forward Secrecy when possible. We also enable HSTS and HPKP. This way wehave a strong and future proof ssl configuration and we get an A+ on the QuallyLabs SSL Test.

I've written an Open Source SSL server test. You can use it to test yourconfiguration, as an addition to the other SSL tests our there. It is fast,shows you all the information so you can make your own informed decision (noratings), and the results are saved so you can compare different settings. Youcan test your site via https://ssldecoder.org.

I've also written a handy tool which notifies you when your certificates areabout to expire. It is open source so you can host it yourself internally andthere is a hosted version available at https://certificatemonitor.org.

I've created a website with Copy-pastable strong cipherssuites for NGINX,Apache, Lighttpd and other software: https://cipherli.st. Handy if you don'twant to read this entire tutorial. This tutorial and https://cipherli.stare updated continuously as new vulnerabilities are discovered.

This tutorial works with the stricter requirements of the SSL Labs test announced on the 21st of January 2014 (It already did before that, if you follow(ed) it you get an A+)

You can find more info on the topics by following the links below:

• [Perfect Forward Secrecy][27]
• [Dealing with RC4 and BEAST][28]

We are going to edit the nginx settings in the file /etc/nginx/sites-enabled/yoursite.com (On Ubuntu/Debian) or in /etc/nginx/conf.d/nginx.conf(On RHEL/CentOS).

For the entire tutorial, you need to edit the parts between the server blockfor the server config for port 443 (ssl config). At the end of the tutorial youcan find the complete config example.

Make sure you back up the files before editing them!

SSL Protocols

All protocols other than TLS 1.2 and TLS 1.3 are considered unsafe.

Edit the config file:

The Cipher Suite

Forward Secrecy ensures the integrity of a session key in the event that a long-term key is compromised. PFS accomplishes this by enforcing the derivation of anew key for each and every session.

This means that when the private key gets compromised it cannot be used todecrypt recorded SSL traffic.

The cipher suites that provide Perfect Forward Secrecy are those that use anephemeral form of the Diffie-Hellman key exchange. Their disadvantage is theiroverhead, which can be improved by using the elliptic curve variants.

The following two ciphersuites are recommended by me, and the latter by theMozilla Foundation.

The recommended cipher suite:

The recommended cipher suite for backwards compatibility (IE6/WinXP):

If your version of OpenSSL is old, unavailable ciphers will be discardedautomatically. Always use the full ciphersuite above and let OpenSSL pick theones it supports.

The ordering of a ciphersuite is very important because it decides whichalgorithms are going to be selected in priority. The recommendation aboveprioritizes algorithms that provide perfect forward secrecy.

Older versions of OpenSSL may not return the full list of algorithms. AES-GCMand some ECDHE are fairly recent, and not present on most versions of OpenSSLshipped with Ubuntu or RHEL.

Prioritization logic

• ECDHE+AESGCM ciphers are selected first. These are TLS 1.2 ciphers. No known attack currently target these ciphers.
• PFS ciphersuites are preferred, with ECDHE first, then DHE.
• AES 128 is preferred to AES 256. There has been discussions on whether AES256 extra security was worth the cost , and the result is far from obvious. At the moment, AES128 is preferred, because it provides good security, is really fa st, and seems to be more resistant to timing attacks.
• In the backward compatible ciphersuite, AES is preferred to 3DES. BEAST attacks on AES are mitigated in TLS 1.1 and a bove, and difficult to achieve in TLS 1.0. In the non-backward compatible ciphersuite, 3DES is not present.
• RC4 is removed entirely. 3DES is used for backward compatibility. See discussion in #RC4_weaknesses

Mandatory discards

• aNULL contains non-authenticated Diffie-Hellman key exchanges, that are subject to Man-In-The-Middle (MITM) attacks
• eNULL contains null-encryption ciphers (cleartext)
• EXPORT are legacy weak ciphers that were marked as exportable by US law
• RC4 contains ciphers that use the deprecated ARCFOUR algorithm
• DES contains ciphers that use the deprecated Data Encryption Standard
• SSLv2 contains all ciphers that were defined in the old version of the SSL standard, now deprecated
• MD5 contains all the ciphers that use the deprecated message digest 5 as the hashing algorithm

Extra settings

Make sure you also add these lines:

When choosing a cipher during an SSLv3 or TLSv1 handshake, normally the client'spreference is used. If this directive is enabled, the server's preference willbe used instead.

Forward Secrecy & Diffie Hellman Ephemeral Parameters

The concept of forward secrecy is simple: client and server negotiate a key thatnever hits the wire, and is destroyed at the end of the session. The RSA privatefrom the server is used to sign a Diffie- Hellman key exchange between theclient and the server. The pre-master key obtained from the Diffie-Hellmanhandshake is then used for encryption. Since the pre-master key is specific to aconnection between a client and a server, and used only for a limited amount oftime, it is called Ephemeral.

With Forward Secrecy, if an attacker gets a hold of the server's private key, itwill not be able to decrypt past communications. The private key is only used tosign the DH handshake, which does not reveal the pre- master key. Diffie-Hellmanensures that the pre-master keys never leave the client and the server, andcannot be intercepted by a MITM.

All versions of nginx as of 1.4.4 rely on OpenSSL for input parameters toDiffie-Hellman (DH). Unfortunately, this means that Ephemeral Diffie- Hellman(DHE) will use OpenSSL's defaults, which include a 1024-bit key for the key-exchange. Since we're using a 2048-bit certificate, DHE clients will use aweaker key-exchange than non-ephemeral DH clients.

We need generate a stronger DHE parameter:

And then tell nginx to use it for DHE key-exchange:

OCSP Stapling

When connecting to a server, clients should verify the validity of the servercertificate using either a Certificate Revocation List (CRL), or an OnlineCertificate Status Protocol (OCSP) record. The problem with CRL is that thelists have grown huge and takes forever to download.

OCSP is much more lightweight, as only one record is retrieved at a time. Butthe side effect is that OCSP requests must be made to a 3rd party OCSP responderwhen connecting to a server, which adds latency and potential failures. In fact,the OCSP responders operated by CAs are often so unreliable that browser willfail silently if no response is received in a timely manner. This reducessecurity, by allowing an attacker to DoS an OCSP responder to disable thevalidation.

The solution is to allow the server to send its cached OCSP record during theTLS handshake, therefore bypassing the OCSP responder. This mechanism saves aroundtrip between the client and the OCSP responder, and is called OCSPStapling.

The server will send a cached OCSP response only if the client requests it, byannouncing support for the status_request TLS extension in its CLIENT HELLO.

Most servers will cache OCSP response for up to 48 hours. At regular intervals,the server will connect to the OCSP responder of the CA to retrieve a fresh OCSPrecord. The location of the OCSP responder is taken from the AuthorityInformation Access field of the signed certificate.

HTTP Strict Transport Security

When possible, you should enable HTTP Strict Transport Security (HSTS),which instructs browsers to communicate with your site only over HTTPS.

HTTP Public Key Pinning Extension

You should also enable the HTTP Public Key Pinning Extension.

Public Key Pinning means that a certificate chain must include a whitelistedpublic key. It ensures only whitelisted Certificate Authorities (CA) can signcertificates for *.example.com, and not any CA in your browser store.

I've written an article about it that has background theory and configurationexamples for Apache, Lighttpd and NGINX: https://raymii.org/s/articles/HTTPPublic Key Pinning Extension_HPKP.html

Poodle and TLS-FALLBACK-SCSV

SSLv3 allows exploiting of the POODLE bug. This is one more major reasonto disable this.

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Google have proposed an extension to SSL/TLS named TLS FALLBACK SCSVthat seeks to prevent forced SSL downgrades. This is automatically enabled ifyou upgrade OpenSSL to the following versions:

Diffie-hellman Dh Key How Long Generate Code

• OpenSSL 1.0.1 has TLS FALLBACK SCSV in 1.0.1j and higher.
• OpenSSL 1.0.0 has TLS FALLBACK SCSV in 1.0.0o and higher.
• OpenSSL 0.9.8 has TLS FALLBACK SCSV in 0.9.8zc and higher.

The BEAST attack and RC4

In short, by tampering with an encryption algorithm's CBC - cipher blockchaining - mode's, portions of the encrypted traffic can be secretly decrypted.More info on the above link.

Recent browser versions have enabled client side mitigation for the beastattack. The recommendation was to disable all TLS 1.0 ciphers and only offerRC4. However, [RC4 has a growing list of attacks againstit],(http://www.isg.rhul.ac.uk/tls/) many of which have crossed the line fromtheoretical to practical. Moreover, there is reason to believe that the NSA hasbroken RC4, their so-called 'big breakthrough.'

Diffie Hellman Generator

Disabling RC4 has several ramifications. One, users with shitty browsers such asInternet Explorer on Windows XP will use 3DES in lieu. Triple- DES is moresecure than RC4, but it is significantly more expensive. Your server will paythe cost for these users. Two, RC4 mitigates BEAST. Thus, disabling RC4 makesTLS 1.0 users susceptible to that attack, by moving them to AES-CBC (the usualserver-side BEAST 'fix' is to prioritize RC4 above all else). I am confidentthat the flaws in RC4 significantly outweigh the risks from BEAST. Indeed, withclient-side mitigation (which Chrome and Firefox both provide), BEAST is anonissue. But the risk from RC4 only grows: More cryptanalysis will surface overtime.

Factoring RSA-EXPORT Keys (FREAK)

FREAK is a man-in-the-middle (MITM) vulnerability discovered by a group ofcryptographers at INRIA, Microsoft Research and IMDEA. FREAK stands for'Factoring RSA-EXPORT Keys.'

The vulnerability dates back to the 1990s, when the US government banned sellingcrypto software overseas, unless it used export cipher suites which involvedencryption keys no longer than 512-bits.

It turns out that some modern TLS clients - including Apple's SecureTransportand OpenSSL - have a bug in them. This bug causes them to accept RSA export-grade keys even when the client didn't ask for export-grade RSA. The impact ofthis bug can be quite nasty: it admits a 'man in the middle' attack whereby anactive attacker can force down the quality of a connection, provided that theclient is vulnerable and the server supports export RSA.

There are two parts of the attack as the server must also accept 'export gradeRSA.'

The MITM attack works as follows:

• In the client's Hello message, it asks for a standard 'RSA' ciphersuite.
• The MITM attacker changes this message to ask for 'export RSA'.
• The server responds with a 512-bit export RSA key, signed with its long-term key.
• The client accepts this weak key due to the OpenSSL/SecureTransport bug.
• The attacker factors the RSA modulus to recover the corresponding RSA decryption key.
• When the client encrypts the 'pre-master secret' to the server, the attacker can now decrypt it to recover the TLS 'm aster secret'.
• From here on out, the attacker sees plaintext and can inject anything it wants.

The ciphersuite offered here on this page does not enable EXPORT grade ciphers.Make sure your OpenSSL is updated to the latest available version and urge yourclients to also use upgraded software.

Logjam (DH EXPORT)

Researchers from several universities and institutions conducted a studythat found an issue in the TLS protocol. In a report the researchers report twoattack methods.

Diffie-Hellman key exchange allows that depend on TLS to agree on a shared keyand negotiate a secure session over a plain text connection.

With the first attack, a man-in-the-middle can downgrade a vulnerable TLSconnection to 512-bit export-grade cryptography which would allow the attackerto read and change the data. The second threat is that many servers and use thesame prime numbers for Diffie-Hellman key exchange instead of generating theirown unique DH parameters.

The team estimates that an academic team can break 768-bit primes and that anation-state could break a 1024-bit prime. By breaking one 1024-bit prime, onecould eavesdrop on 18 percent of the top one million HTTPS domains. Breaking asecond prime would open up 66 percent of VPNs and 26 percent of SSH servers.

Later on in this guide we generate our own unique DH parameters and we use aciphersuite that does not enable EXPORT grade ciphers. Make sure your OpenSSL isupdated to the latest available version and urge your clients to also useupgraded software. Updated browsers refuse DH parameters lower than 768/1024 bitas a fix to this.

Cloudflare has a detailed guide on logjam.

Heartbleed

Heartbleed is a security bug disclosed in April 2014 in the OpenSSL cryptographylibrary, which is a widely used implementation of the Transport Layer Security(TLS) protocol. Heartbleed may be exploited regardless of whether the partyusing a vulnerable OpenSSL instance for TLS is a server or a client. It resultsfrom improper input validation (due to a missing bounds check) in theimplementation of the DTLS heartbeat extension (RFC6520), thus the bug's namederives from 'heartbeat'. The vulnerability is classified as a buffer over-read,a situation where more data can be read than should be allowed.

What versions of the OpenSSL are affected by Heartbleed?

Status of different versions:

• OpenSSL 1.0.1 through 1.0.1f (inclusive) are vulnerable
• OpenSSL 1.0.1g is NOT vulnerable
• OpenSSL 1.0.0 branch is NOT vulnerable
• OpenSSL 0.9.8 branch is NOT vulnerable

The bug was introduced to OpenSSL in December 2011 and has been out in the wildsince OpenSSL release 1.0.1 on 14th of March 2012. OpenSSL 1.0.1g released on7th of April 2014 fixes the bug.

By updating OpenSSL you are not vulnerable to this bug.

Diffie-hellman Dh Key How Long Generate Number

SSL Compression (CRIME attack)

The CRIME attack uses SSL Compression to do its magic. SSL compression is turnedoff by default in nginx 1.1.6+/1.0.9+ (if OpenSSL 1.0.0+ used) and nginx1.3.2+/1.2.2+ (if older versions of OpenSSL are used).

If you are using al earlier version of nginx or OpenSSL and your distro has notbackported this option then you need to recompile OpenSSL without ZLIB support.This will disable the use of OpenSSL using the DEFLATE compression method. Ifyou do this then you can still use regular HTML DEFLATE compression.

Conclusion

Diffie Hellman Key Exchange Example

If you have applied the above config lines you need to restart nginx:

Now use the SSL Labs test to see if you get a nice A. And, of course, havea safe, strong and future proof SSL configuration!

Diffie-hellman Dh Key How Long Generate Pdf