ECM Handler

Create and view encrypted messages using a URL-like data scheme. Possibilities include:
- exchange private information over unsafe channels: email, QR codes...
- compress text data, with or without a password, and use the output inside a QR code.

All messages are encrypted using AES with a 256-bit key in CBC mode. Passwords are derived using PBKDF2 with 8192 iterations, with a double salt added. Data integrity is verified by its MD5 checksum after decryption. So everything is safe.

The encoded message has 2 parts:
- the scheme prefix: ecm:// followed by a 1 character reserved header
- the encoded data - currently using a subset of Kanji characters, in order to allow a potentially maximum data compression inside a QR code (each Kanji char would be encoded directly to 13-bits, whereas using UTF-8 would be a masive overhead - ~3 bytes/character)

*** Note that currently the available QR encoders do not efficiently create the smallest possible QR symbol when provided with a string that contains many consecutive Kanji characters (as in the case of an ECM string), but treat it as a UTF-8 string. This is something that should be addressed to the QR encoders authors, since its perfectly valid to have two different data segments inside a QR code. The ECM data format only guarantees that everything after the (ecm:// + header) is valid to be encoded in Kanji mode (only contains valid characters in the 0x8140-0xEBBF Shift_JIS charset range).

Keywords: encryption, security.