An easy way to encrypt and decrypt large files using OpenSSL and Linux:

Generate PEM public private key using openssl:

openssl req -x509 -nodes -newkey rsa:2048 -keyout private-key.pem -out public-key.pem

Encrypt file using public key PEM file:

openssl smime -encrypt -binary -aes-256-cbc -in large_file.img -out large_file.img.dat -outform DER public-key.pem

We can generate hash using md5sum for both files so we can compare them once we decrypt our file:

md5sum large_file.img*
 #cd573cfaace07e7949bc0c46028904ff  large_file.img
 #c4d8f1e868d1176d8aa5363b0bdf8e7c  large_file.img.dat

Decrypt large file using OpenSSL:

openssl smime -decrypt -in large_file.img.dat -binary -inform DEM -inkey private-key.pem -out decrypted_large_file.img

Check md5sum output:

md5sum *large_file.img*
 #cd573cfaace07e7949bc0c46028904ff  decrypted_large_file.img
 #cd573cfaace07e7949bc0c46028904ff  large_file.img
 #c4d8f1e868d1176d8aa5363b0bdf8e7c  large_file.img.dat

#linux #openssl #pem #encryption #decryption #x509 #public_key #private_key