Also note that the encryption and decryption operations performed by DBMS_CRYPTO occur on the server, not on the client. Application developers must take care to ensure that the encryption keys used with this package are securely generated and stored. The DBMS_CRYPTO package can generate random material for encryption keys, but it does not provide a mechanism for maintaining them. A virus cannot do that with a MAC because the virus does not know the key.Ībout Generating and Storing Encryption Keys If the user did not use a MAC function, then the virus could compute the new hash value after infection and replace the table entry. A user could compute the MAC of his files and store that value in a table. They can also be used by a single user to determine if her files have been altered, perhaps by a virus. MACs can be used to authenticate files between users. It works the same way as the DBMS_CRYPTO.HASH function, except only someone with the key can verify the hash value. The MAC function is also a one-way hash function, but with the addition of a secret key. The HASH function included with DBMS_CRYPTO, is a one-way hash function that you can use to generate a hash value from either RAW or LOB data. Hash values are similar to "file fingerprints" and are used to ensure data integrity. If the second hash value is identical to the first one, then the data has not been altered. On returning the stored data, the user can again run the hash function against it, using the same algorithm. For example, before storing data, the user runs DBMS_CRYPTO.HASH against the stored data to create a hash value. You can use hash values to verify whether data has been altered. Note that hash values should be at least 128 bits in length to be considered secure. It is easy to compute a hash value from an input message, but it is extremely difficult to generate an input message that hashes to a particular value. One-way hash functions work in one direction only. Hash functions operate on an arbitrary-length input message, and return a fixed-length hash value. ![]() ![]() This package includes two different types of one-way hash functions: the HASH function and the MAC function. When to Use Hash or Message Authentication Code (MAC) Functions ,iv => hextoraw(DBMS_CRYPTO.LEGACY_DEFAULT_IV) If you are using DBMS_CRYPTO to decipher a triple-DES ciphertext that you created in the past using the desupported DBMS_OBFUSCATION_TOOLKIT, then set the typ argument of DBMS_crypt to the value DBMS_CRYPTO.DES3_CBC_NONE to ensure that the PKCS#5 padding is disabled. ,iv => hextoraw(dbms_crypto.LEGACY_DEFAULT_IV) (src => ciphertext_from_legacy_DES3Encrypt If you did not provide the IV argument when creating a triple-DES ciphertext using the desupported DBMS_OBFUSCATION_TOOLKIT, then provide IV as hextoraw(DBMS_CRYPTO.LEGACY_DEFAULT_IV) when invoking DBMS_CRYPTO to decrypt the triple-DES ciphertext.įor example: plaintext := DBMS_crypt
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