% openssl, certificate, encryption

## General OpenSSL Commands
# Create a new signing request and key
openssl req -new -newkey rsa:<RSA_LENGTH> -nodes -out <OUTPUT_CSR> -keyout <OUTPUT_KEY>

# Create a new self-signed certificate
openssl req -x509 -sha256 -nodes -days <VALIDITY> -newkey rsa:<RSA_LENGTH> -out <OUTPUT_CRT> -keyout <OUTPUT_KEY>

# Create a signing request from existing key
openssl req -out <OUTPUT_CSR> -key <INPUT_KEY> -new

# Create a signing request from existing certificate and key
openssl x509 -x509toreq -out <OUTPUT_CSR> -in <INPUT_CRT> -signkey <INPUT_KEY>

# Remove a passphrase from a private key
openssl rsa -in <INPUT_KEY> -out <OUTPUT_PLAINTEXT_KEY>



## Converting between the different encoding
# Convert a DER encoded file to a PEM encoded file
openssl x509 -inform der -in <INPUT_CRT> -out <OUTPUT_PEM>

# Convert a PEM encoded file to a DER encoded file
openssl x509 -outform der -in <INPUT_PEM> -out <OUTPUT_CRT>

# Convert a PKCS12 encoded file containing a private key and certificates to PEM
openssl pkcs12 -in <INPUT_PKCS12> -out <OUTPUT_PEM> -nodes

# Extract the private key from a PKCS12 encoded file
openssl pkcs12 -in <INPUT_PKCS12> -out <OUTPUT_PEM> -nodes -nocerts

# Extract the certificate from a PKCS12 encoded file
openssl pkcs12 -in <INPUT_PKCS12> -out <OUTPUT_PEM> -nodes -nokeys

# Convert a PEM certificate file and a private key to PKCS12 encoded file
openssl pkcs12 -export -out <OUTPUT_PKCS12> -inkey <INPUT_KEY> -in <INPUT_CRT> -certfile <INPUT_CRT>



## Validating certificates and keys using OpenSSL
# Validate a certificate signing request
openssl req -text -noout -verify -in <OUTPUT_CSR>

# Validate a private key
openssl rsa -in <INPUT_KEY> -check

# Validate a certificate
openssl x509 -in <INPUT_CRT> -text -noout

# Validate a PKCS12 file (.pfx or .p12)
openssl pkcs12 -info -in <INPUT_PKCS12>



## Debugging using OpenSSL
# Compare the MD5 hash of a certificate
openssl x509 -noout -modulus -in <INPUT_CRT> | openssl md5

# Compare the MD5 hash of a private key
openssl rsa -noout -modulus -in <INPUT_KEY> | openssl md5

# Compare the MD5 hash of a certificate signing request
openssl req -noout -modulus -in <INPUT_CSR> | openssl md5

# Display the server certificate chain
openssl s_client -connect <URL>:<PORT>



# Sensible/common default alternatives
$ VALIDITY: printf "DAYS\tCOMMENT\n1\ta day\n30\ta month\n365\ta year\n730\ttwo years" --- --column 1 --headers 1
$ RSA_LENGTH: printf "KEY LENGTH\tCOMMENT\n2048\t\tDefault\n4096\t\tBetter\n8192\t\tSlow?" --- --column 1 --headers 1

# Attempt to find files with the appropriate endings, default to everything.
$ INPUT_PKCS12: ls -a | grep -e "\(.pfx\|.p12\)"       || ls -a
$ INPUT_CSR:    ls -a | grep -e "\(.csr\)"             || ls -a
$ INPUT_KEY:    ls -a | grep -e "\(.key\|.pem\)"       || ls -a
$ INPUT_CRT:    ls -a | grep -e "\(.crt\|.cer\|.der\)" || ls -a
$ INPUT_PEM:    ls -a | grep -e "\(.pem\)"             || ls -a