Database Reference
In-Depth Information
none : Not actually encrypted. Use this value for fields you don't care if
an attacker sees, or numeric fields that aren't meaningful on their own.
pseudonym : This is the simplest encryption mode that always encrypts
the same data the same way, given a particular key. This allows you to
check whether two values are equal, lets you JOIN on encrypted values,
and lets you GROUP BY the encrypted values. The downside is that this
type of field can be vulnerable to attackers who can use correlation
attacks or known-frequency attacks to find out the plaintext. Once they
have decrypted the value once, they know everywhere it appears.
probabalistic : Encrypts the same text differently every time. This
makes it harder for known-plaintext and correlation attacks to operate.
homomorphic : Encrypts numeric fields with special mathematical
properties that allow mathematical operations (specifically, sums) to be
performed on the encrypted data that yield an encrypted result.
searchwords : Encrypts data such that you can find a particular word
within a longer string. Note that each individual word will be encrypted
the same way each time, so this can allow known plaintext attacks or
linguistic frequency attacks. The advantage of this type of encryption is
that it lets you find records that have a particular word embedded in a
longer string without the query engine seeing anything except encrypted
data.
probabilistic_searchwords : Combines probabilistic encryption
with searchwords encryption. Encrypts each separate word with
probabilistic encryption, so it will be different each time. This allows
you to pull out individual words and compare them.
Attacks Against Encrypted Data
We've mentioned a lot of attacks against the encryption; what do these
actually mean? An active attacker can glean information about encrypted
data without being able to break the encryption directly. For example, say
that an attacker has access to an encrypted table and wants to know the
words that are used in Macbeth . The attacker knows that there are six
Shakespeare plays where the name of the play is also a character, one of
which is Macbeth . He could use this information to find the rows in the table
where the corpus field equals the word field. He might also know that of
the six plays where the name of the play is also a character, only two were
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