1. Openssl Client Server Example C#
  2. Openssl Examples
  3. C Openssl Rsa Example
  4. Openssl C++ Example
  5. Openssl.net C# Example

From time to time it may be necessary to verify what certificate is being presented by the server that you are connecting to. Sometimes this is a SMTP server or it could be a web server. While there are multiple methods that can be used to validate a certificate presented from a server I am going to be focusing on openssl here.

OpenSSL is a robust, commercial-grade, and full-featured toolkit for the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols. OpenSSL is available for multiple platforms including Linux, MacOS & Windows (via gnuwin32). The SSL handshake is an authentication process. In which server and client authenticate to each other using a certificate. This certificate is generated by the user own self with the help of OpenSSL commands or it is provided by a third party (certificate authority). C# (CSharp) OpenSSL.Core BIO - 30 examples found. These are the top rated real world C# (CSharp) examples of OpenSSL.Core.BIO extracted from open source projects. You can rate examples to help us improve the quality of examples. If the OpenSSL headers are in the openssl sub-directory of the current directory, use.o Opentest Opentest.c -lcrypto The pre-processor looks to create a name such as './openssl/ssl.h' from the '.' In the -I option and the name specified in angle brackets.

OpenSSL is a robust, commercial-grade, and full-featured toolkit for the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols. OpenSSL is available for multiple platforms including Linux, MacOS & Windows (via gnuwin32). For this article I will be using the Windows version of OpenSSL which can be downloaded from http://gnuwin32.sourceforge.net/packages/openssl.htm.

The syntax that we use depends on what type of server we are querying. To query a web server you would do the following:

To query a smtp server you would do the following:

Where <server> is replaced with the fully qualified domain name (FQDN) of the server we want to check. The output generated contains multiple sections with --- spearators between them. The following example is showing a connection on port 443 against outlook.office365.com. The first section presented is around the connection information:

The next section contains details about the certificate chain:

The actual public server certificate is next:

Following the server certificate we see the Certificate Subject and Issuer:

If there is a client certificate sent it would be presented next:

We next see details about the particular SSL handshake that occurred:

Openssl Client Server Example C#

Next if we query a SMTP server on port 25 with the -starttls smtp parameters we will get back the information from that server. Below is an example of one of the output from this type of query:

In both of these examples the typical information that we use in troubleshooting is the certifcate chain.
e.g. 1:

e.g. 2:

Depending on the problem I'm dealing with I'll make a determination on how I want to proceed next. If the system you are connecting from is receiving regular root certificate updates there shouldn't be any issues with the root certificates.

The most common issue that I see around certificates is missing root certificates. These problems are easily resolved by ensuring that you have installed the most recent root certificate update for your system.

Openssl C# Example

If you find that the proper root certificates have been installed on the system the next thing to check is that you can reach the certificate revolcation list (CRL) to verify that the certificate is still valid. This requires internet access and on a Windows system can be checked using certutil.

At the very bottom of the output you should see:

If you don't have access to the internet you will see an error at this point.

For one of the Matasano crypto challenges, I had to decrypt the text which was encrypted using AES in ECB mode. Everything about AES is actually documented by the National Institute of Standards and Technology. You can get all the algorithms behind AES encryption. It is probably not a good idea to implement it from scratch.Openssl has a well tested and widely used library which works.

Openssl C# Example

This Openssl library page gives a complete example of how to use them. There are a few preparatory steps before you can use the instructions though. These instructions are for Ubuntu like Linux distributions. These worked well on my Raspberry Pi too.

Installing Openssl library

Following command installs all the C libraries needed to use Openssl with your C code.

Openssl Examples

For example, you will want to include the following header files:

C Openssl Rsa Example

Compiling your C program with the Openssl library

Next, you can follow the instructions from the Openssl crypto library page to create your C program. I have an example program in my CrytopalsGithub repository. While linking the program you need to provide the ssl and crypto library names. Following command should do it:

A few pointers on the do_crypt function

Openssl C++ Example

  • If you are going to use the do_crypt function for decrypting a text encrypted using electronic code book (ECB) mode, you should remove the following assert line since there is no Initialization Vector for ECB.

Openssl.net C# Example

  • The example code operates on the raw data. So, if you are trying to decrypt the data which is base64 encoded, your first step should be to convert it into raw data.
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