APC025 PROPER CODE DETECT USING LOW SPEED DATA
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2002-Apr-11
Encryption is used to protect information in sys- tems where sensitive audio is transmitted over the air. In order for the receiving radio to successfully decrypt an encrypted transmission, the receiving radio must have the algorithm and the key that was used in the encryption process. The APC025 Com- mon Air Interface provides an ALGID (Algorithm ID) Field and a KID (Key Identifier) Field to indentily the algorithm and the key that was used to encrypt the transmitted signal, Ifthe receiving radio has the matching KID and ALGID, the received audio is decrypted and routed to the speaker. The problem with this approach is that a matching KID and ALGID does not guarantee that the correct key will be used to decrypt the audio signal. It merely indi- cates that the KID and ALGID matches. The actual key data associated with the KEYID may be differ- ent (e.g. transmitting radio maps KID = 1 to the key Ox012356789ABDEF but receiving radio maps KID = 1 to the key OxABCDEFO123456789). There- fore an attempt to decrypt the audio signal will result in noise being routed to the speaker.