OpenSSL

Another great tool to check SSL stuff is https://testssl.sh/

Create certificates and keys

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 (see How to Create and Install an Apache Self Signed Certificate for more info)

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

Create dhparam

openssl dhparam -out /usr/local/etc/ssl/dhparam.pem 4096

Remove Passphrase from SSL Key

openssl rsa -in www.key -out new.key

Validate Certificates and Keys

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: This displays all (including Intermediates) certificates of a given website.

openssl s_client -connect www.google.com:443

Check Certificate

openssl x509 -in certificate.crt -text -noout

Check CSR of Certificate

Decode your Certificate Signing Request (CSR) and and verify that it contains the correct information:

openssl req -in mycsr.csr -noout -text

Check a private key

openssl rsa -in private.key -check

Check a PKCS#12 file (.pfx or .p12)

openssl pkcs12 -info -in keyStore.p12

Converting Using OpenSSL

Convert certificates and keys to different formats to make them compatible with OS/software required.

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

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

openssl pkcs12 -in keyStore.pfx -out keyStore.pem -nodes

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

How to encrypt and decrypt files with OpenSSL

Install openssl and the associated development libraries'

Run openssl version -a to check if openssl is installed or just run this command to install all requirements for this demo:

sudo apt install libssl-dev openssl

Create a test file named "plain.txt" which we shall encrypt & decrypt in the next step.

echo "this is a test" > plain.txt

Encrypt and Decrypt example via Triple Data Encryption Standard

The following lines will create the encrypted file "encrypted.txt" and decrypted file "decrypted.txt".

openssl des3 -in plain.txt -out encrypted.txt -pass pass:password
openssl des3 -d -in encrypted.txt -out decrypted.txt -pass pass:password

The file "decrypted.txt" should match with our test file "plain.txt".

diff -s plain.txt decrypted.txt

Encrypt and Decrypt example via AES-256 with CBC

There are plenty of ciphers availble. Run openssl help to see the cipher commands available too you. Here is another example using AES-256 with CBC.

openssl aes-256-cbc -a -salt -in plain.txt -out encrypted.txt -k password
openssl aes-256-cbc -d -a -in encrypted.txt -out decrypted.txt -k password

Encrypt images using a key and IV

openssl aes-128-cbc -K "55555555555555555555555555555555" -iv "83deccd3f93b37c70d37297f319cf367" -in WRxFKdq.png -out OMG_SAME_IMAGE.png

Example screenshot:

HTTPS webserver

openssl req -x509 -newkey rsa:4096 -keyout /tmp/key.pem -out /tmp/cert.pem -nodes && openssl s_server -WWW -port 8443 -cert /tmp/cert.pem -key /tmp/key.pem

openssl req -newkey rsa:2048 -nodes -x509 -subj '/CN=name-you-want.example.com' -days 3650 -out server.cert -keyout server.key

openssl s_server -accept 7781 -cert server.cert -key server.key -WWW

Extract a certificate and private key from PFX file

CertName='cert.pfx'
openssl pkcs12 -in $PfxCert -nocerts -out key.pem -nodes #Export the private key
openssl pkcs12 -in $PfxCert -nokeys -out $CertName.pem #Export the certificate
openssl rsa -in key.pem -out $CertName.key #Remove the passphrase from the private key

Create a random password

openssl rand -base64 32