I

initialization vector

(IV) A sequence of random bytes appended to the front of the plaintext before encryption by a block cipher. Adding the initialization vector to the beginning of the plaintext eliminates the possibility of having the initial ciphertext block the same for any two messages.

For example, if messages always start with a common header (a letterhead or "From" line) their initial ciphertext would always be the same, assuming that the same cryptographic algorithm and symmetric key was used. Adding a random initialization vector eliminates this from happening.

inner data

Any encoded data used as the message for another encoded message. For example, an enveloped message and its hash value may be the inner data for a second message.

inner content

Data that is enhanced, such as with a digital signature. This term is used primarily when discussing enhanced data in a PKCS #7 message.

integrity

The completeness and accuracy of a message after it has been sent or stored.

IV

See initialization vector.