OpenSSL is a software library for applications that secure communications over computer networks against eavesdropping or need to identify the party at the other end. It is widely used in Internet web servers, serving a majority of all websites.

OpenSSL contains an open-source implementation of the SSL and TLS protocols. The core library, written in the C programming language, implements basic cryptographic functions and provides various utility functions. Wrappers allowing the use of the OpenSSL library in a variety of computer languages are available.

Versions are available for most Unix and Unix-like operating systems (including Solaris, Linux, macOS, QNX, and the various open-source BSD operating systems), OpenVMS and Microsoft Windows. IBM provides a port for the System I (OS/400). source: Wikipedia

For Windows System, you can download and install OpenSSL Application on this link.

Below is the most command that we can use for OpenSSL operation.

  • Generate a new private key and Certificate Signing Request 
    openssl req -out CSR.csr -new -newkey rsa:2048 -nodes -keyout privateKey.key
  • Generate a self-signed certificate 
    openssl req -x509 -sha256 -nodes -days 365 -newkey rsa:2048 -keyout privateKey.key -out certificate.crt
  • Generate a certificate signing request (CSR) for an existing private key
    openssl req -out CSR.csr -key privateKey.key -new
  • Generate a certificate signing request based on an existing certificate
    openssl x509 -x509toreq -in certificate.crt -out CSR.csr -signkey privateKey.key
  • Remove a passphrase from a private key
    openssl rsa -in privateKey.pem -out newPrivateKey.pem
  • Check a Certificate Signing Request (CSR)
    openssl req -text -noout -verify -in CSR.csr
  • Check a private key
    openssl rsa -in privateKey.key -check
  • Check a certificate
    openssl x509 -in certificate.crt -text -noout
  • Check a PKCS#12 file (.pfx or .p12)
    openssl pkcs12 -info -in keyStore.p12
  • Check an MD5 hash of the public key to ensure that it matches with what is in a CSR or private key
    openssl x509 -noout -modulus -in certificate.crt | openssl md5
    openssl rsa -noout -modulus -in privateKey.key | openssl md5
    openssl req -noout -modulus -in CSR.csr | openssl md5
  • Check an SSL connection. All the certificates (including Intermediates) should be displayed
    openssl s_client -connect www.paypal.com:443
  • Convert a DER file (.crt .cer .der) to PEM
    openssl x509 -inform der -in certificate.cer -out certificate.pem
  • Convert a PEM file to DER
    openssl x509 -outform der -in certificate.pem -out certificate.der
  • Convert a PKCS#12 file (.pfx .p12) containing a private key and certificates to PEM
    openssl pkcs12 -in keyStore.pfx -out keyStore.pem -nodes

    You can add –nocerts to only output the private key or add –nokeys to only output the certificates.

  • Convert a PEM certificate file and a private key to PKCS#12 (.pfx .p12)
    openssl pkcs12 -export -out certificate.pfx -inkey privateKey.key -in certificate.crt -certfile CACert.crt

source: www.sslshoper.com

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