AES-256 requires a 256-bit key, period. However there are different ways of building that 256-bit key. One way is to generate 256 random bits and take them as the key. You need to store these 256 bits somewhere, or you won't be able to decrypt what you've encrypted. Openssl aes-256-cbc -salt -a -d -in encrypted.txt -out plaintext.txt Asymmetric encryption. For Asymmetric encryption you must first generate your private key and extract the public key. Openssl genrsa -aes256 -out private.key 8912 openssl rsa -in private.key -pubout -out public.key To encrypt.

This page describes the command line tools for encryption and decryption. Enc is used for various block and stream ciphers using keys based on passwords or explicitly provided. It can also be used for Base64 encoding or decoding.

• 4Examples
  • 4.2Encryption

Synopsis[edit]

The basic usage is to specify a ciphername and various options describing the actual task.

You can obtain an incomplete help message by using an invalid option, eg. -help.

Cipher alogorithms[edit]

To get a list of available ciphers you can use the list -cipher-algorithms command

The output gives you a list of ciphers with its variations in key size and mode of operation. For example AES-256-CBC for AES with key size 256 bits in CBC-mode. Some ciphers also have short names, for example the one just mentioned is also known as aes256. These names are case insensitive. In addition none is a valid ciphername. This algorithms does nothing at all.

Options[edit]

The list of options is rather long.

-in filename

This specifies the input file.

-out filename

This specifies the output file. It will be created or overwritten if it already exists.

-e or -d

This specifies whether to encrypt (-e) or to decrypt (-d). Encryption is the default. Of course you have to get all the other options right in order for it to function properly. In particular it is necessary to give the correct cipher-name as well as -a, -A or -z options.

-a, -A, -base64

These flags tell OpenSSL to apply Base64-encoding before or after the cryptographic operation. The -a and -base64 are equivalent. If you want to decode a base64 file it is necessary to use the -d option. By default the encoded file has a line break every 64 characters. To suppress this you can use in addition to -base64 the -A flag. This will produce a file with no line breaks at all. You can use these flags just for encoding Base64 without any ciphers involved.

-bufsize n

Specify the buffer size. This concerns only internal buffers. It has nothing to do with the cryptographic algorithms in question.

-debug

Enable debugging output. This does not include any sensitive information. See also -P.

-engine id

Specify an engine for example to use special hardware.

-iv IV

This specifies the initialization vectorIV as hexadecimal number. If not explicitly given it will be derived from the password. See key derivation for details.

-k password, -kfile filename

Both option are used to specify a password or a file containing the password which is used for key derivation. However they are deprecated. You should use the -pass option instead. The equivalents are -pass pass:password and -pass file:filename respectively.

-K key

This option allows you to set the key used for encryption or decryption. This is the key directly used by the cipher algorithm. If no key is given OpenSSL will derive it from a password. This process is described in PKCS5#5 (RFC-2898).

-md messagedigest

This specifies the message digest which is used for key derivation. It can take one of the values md2, md5, sha or sha1.

-nopad

This disables standard padding.

-salt, -nosalt, -S salt

These options allow to switch salting on or off. With -Ssalt it is possible to explicitly give its value (in hexadecimal).

-p, -P

Additionally to any encryption tasks, this prints the key, initialization vector and salt value (if used). If -P is used just these values are printed, no encryption will take place.

-pass arg

This specifies the password source. Possible values for arg are pass:password or file:filename, where password is your password and filename file containing the password.

-z

Use this flag to enable zlib-compression. After a file is encrypted (and maybe base64 encoded) it will be compressed via zlib. Vice versa while decrypting, zlib will be applied first.

Examples[edit]

Base64 Encoding[edit]

To encode a file text.plain you can use

To decode a file the the decrypt option (-d) has to be used

Encryption[edit]

Basic Usage[edit]

The most basic way to encrypt a file is this

Openssl Generate Aes 256 Key Size

It will encrypt the file some.secret using the AES-cipher in CBC-mode. The result will be Base64 encoded and written to some.secret.enc. OpenSSL will ask for password which is used to derive a key as well the initialization vector.Since encryption is the default, it is not necessary to use the -e option.

Use a given Key[edit]

It also possible to specify the key directly. For most modes of operations (i.e. all non-ECB modes) it is then necessary to specify an initialization vector. Usually it is derived together with the key form a password. And as there is no password, also all salting options are obsolete.

The key and the IV are given in hex. Their length depending on the cipher and key size in question.

The key above is one of 16 weak DES keys. It should not be used in practice.

Generate private key for an SSL certificate and verify its consistency.

Generate unencrypted private key

Generate 4096-bit private key using RSA algorithm.

Generate encrypted private key

Basic way to generate encrypted private key

Generate 4096-bit RSA private key, encrypt it using AES-192 cipher and password provided from the application itself as you will be asked for it.

Different ways to generate encrypted private key

Openssl Generate Random Aes 256 Key

Generate 4096-bit RSA private key, encrypt it using 3DES cipher and password provided from the command-line.

Generate 4096-bit RSA private key, encrypt it using AES-128 cipher and password provided from the specific file.

Generate 4096-bit RSA private key, encrypt it using CAMELLIA-256 cipher and password provided from the environment variable.

Generate 4096-bit RSA private key, encrypt it using AES-256 cipher and password provided from standard input.

Encrypt or decrypt existing private key

Encrypt existing private key using AES-256 cipher and password provided from the command-line.

Re-encrypt existing private key using AES-256 cipher and password provided from the command-line.

Openssl Generate Aes 256 Key Detection

Decrypt existing private key using password provided from the command-line.

Verify consistency of the private key

Verify consistency of the private key using password provided from the command-line.

Openssl Generate Aes 256 Key Base64

Result when private key’s integrity is not compromised.

Result when private key’s integrity is compromised.

Openssl Generate Aes 256 Key

Additional information

You can still use the following command to generate private key.

Openssl Generate Aes 256 Keys

This way is still supported, so existing shell scripts will work without any changes.