![]() This means that unlike for the other streaming-based modes, they operate on fixed-size blocks of data, and therefore they require a “finalization” step to produce or correctly decrypt the last block of data by appropriately handling some form of padding. Calling Cipher#final ¶ ↑ĮCB (which should not be used) and CBC are both block-based modes. As a general rule of thumb, exposing the key directly or indirectly should be avoided at all cost and exceptions only be made with good reason. There are elaborate ways how an attacker can take advantage of such an IV. random_iv # also sets the generated IV on the CipherĪlthough the key is generally a random value, too, it is a bad choice as an IV. A secure random IV can be created as follows cipher =. Think of the IV as a nonce (number used once) - it's public but random and unpredictable. Therefore, ideallyĪlways create a secure random IV for every encryption of your CipherĪ new, random IV should be created for every encryption of data. it may be transmitted in public once generated, it should still stay unpredictable to prevent certain kinds of attacks. Although the IV can be seen as public information, i.e. You should never use ECB mode unless you are absolutely sure that you absolutely need itīecause of this, you will end up with a mode that explicitly requires an IV in any case. ECB mode is the only mode that does not require an IV, but there is almost no legitimate use case for this mode because of the fact that it does not sufficiently hide plaintext patterns. The cipher modes CBC, CFB, OFB and CTR all need an “initialization vector”, or short, IV. If you absolutely need to use passwords as encryption keys, you should use Password-Based Key Derivation Function 2 (PBKDF2) by generating the key with the help of the functionality provided by OpenSSL::PKCS5.pbkdf2_hmac_sha1 or OpenSSL::PKCS5.pbkdf2_hmac.Īlthough there is Cipher#pkcs5_keyivgen, its use is deprecated and it should only be used in legacy applications because it does not use the newer PKCS#5 v2 algorithms. random_key # also sets the generated key on the Cipher ![]() A simple and secure way to create a key for a particular Cipher is cipher = OpenSSL :: AES256. There are a lot of ways to create insecure keys, the most notable is to simply take a password as the key without processing the password further. Symmetric encryption requires a key that is the same for the encrypting and for the decrypting party and after initial key establishment should be kept as private information. This should be the first call after creating the instance, otherwise configuration that has already been set could get lost in the process. Still, after obtaining a Cipher instance, we need to tell the instance what it is that we intend to do with it, so we need to call either cipher. new( :CBC)Ĭhoosing either encryption or decryption mode ¶ ↑Įncryption and decryption are often very similar operations for symmetric algorithms, this is reflected by not having to choose different classes for either operation, both can be done using the same class. new( :CBC)Ĭipher = OpenSSL :: Cipher :: AES256. new( :CBC)Ĭipher = OpenSSL :: Cipher :: AES192. new( '128-CBC')įinally, due to its wide-spread use, there are also extra classes defined for the different key sizes of AES cipher = OpenSSL :: Cipher :: AES128. new( 128, 'CBC')Ĭipher = OpenSSL :: Cipher :: AES. new( 128, :CBC)Ĭipher = OpenSSL :: Cipher :: AES. to obtain an instance of AES, you could also use # these are equivalent cipher = OpenSSL :: Cipher :: AES. new( 'AES-128-CBC')įor each algorithm supported, there is a class defined under the Cipher class that goes by the name of the cipher, e.g. Either all uppercase or all lowercase strings may be used, for example: cipher = OpenSSL :: Cipher. That is, a string consisting of the hyphenated concatenation of the individual components name, key length and mode. The most generic way to create a Cipher is the following cipher = OpenSSL :: Cipher. Generally, a Cipher algorithm is categorized by its name, the key length in bits and the cipher mode to be used. There are several ways to create a Cipher instance. Listing all supported algorithms ¶ ↑Ī list of supported algorithms can be obtained by puts OpenSSL :: Cipher. ![]() The algorithms that are available depend on the particular version of OpenSSL that is installed. Provides symmetric algorithms for encryption and decryption.
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