Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

DecryptByKey
Like its asymmetric and certificate based brethren, this one decrypts a chunk of data utilizing a key. What’s
different is that this one not only expects a symmetric key (instead of the other types of key), but it also
expects that key to already be “open” (using the OPEN SYMMETRIC KEY command). Other than that, it is
fairly similar in use, with the encrypted data (either as a literal string or a string coercible variable) fed
in as a parameter and, in this case, a hash key optionally accepted as an authenticator:
DecryptByKey({‘’|},
[, ‘’|])
Note that if you provide an add authenticator value (in the form of an int), that value must match the value
supplied when the string was encrypted, and you must also supply a hash value that matches the hash
supplied at encryption time.
DecryptByPassPhrase
Like the name says, this one decrypts data that was encrypted not by a formal key, but by a passphrase.
Other than accepting a passphrase parameter instead of assuming an open key, DecryptByPassPhrase
works almost exactly like DecryptByKey:
DecryptByPassPhrase({‘’|},
{‘’|},
[, ‘’|])
As with DecryptByKey, if you provide an add authenticator value (in the form of an int), that value must
match the value supplied when the string was encrypted, and you must also supply a hash value that
matches the hash supplied at encryption time.
EncryptByAsmKey
Encrypts a chunk of data utilizing an asymmetric key. It requires the key (by ID) and the data to be
encrypted (either as a literal string or a string coercible variable). The syntax is straightforward enough:
EncryptByAsymKey(, {‘’|})
Keep in mind that if a password was utilized when the asymmetric key was added to the database, the
same password will be required to properly decrypt any data encrypted using that key.
EncryptByCert
Apendix A: System Functions
This is basically the same as EncryptByAsmKey, except that it expects a certificate rather than an asymmetric
key. Like EncryptByAsmKey, this one encrypts a chunk of data utilizing the provided key. It
requires the certificate (by ID), the data to be encrypted (either as a literal string or a string coercible
variable), and optionally, the password to be used to further encrypt the data. The syntax looks almost
just like EncryptByAsymKey:
EncryptByCert(, {‘’|}
[, ‘’])
Again, any password utilized when encrypting the data will be needed to properly decrypt it.
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