The default crypt method for Type 4 is V2, which uses RC4
algorithm. Crypt method settings are in effect only when Type is 4 or higher.
The StringMethod and StreamMethod parameters can take any of the
- 0 [None] – (Not supported)
- 1 [Identity] – No encryption
- 2 [V2] – Uses the RC4 algorithm
- 3 [AESV2] – Uses the AES algorithm with 128-bit encryption
- 4 [AESV3] – Uses the AES algorithm with 256-bit encryption
Adobe Reader does not support using more than one crypt method
per document (i.e. stringMethod≠streamMethod). However, Identity is
degenerate and can be used with other crypt methods.