Crypto phone

Crypto phones are mobile telephones that provide security against eavesdropping and electronic surveillance.

The interception of telecommunications has become a major industry. Most of the world's intelligence agencies and many private organisations intercept telephone communications to obtain military, economic and political information. The price of simple mobile phone surveillance devices has become so low that many individuals can afford to use them.^[1]^[2] Advances in technology have made it difficult to determine who is intercepting and recording private communications.

Crypto phones can protect calls from interception by using algorithms to encrypt the signals. The phones have a cryptographic chip that handles encryption and decryption. Two algorithms are programmed into the chip: A key-exchange algorithm for the key agreement protocol and a symmetric-key algorithm for voice encryption.

Prevention

For the system to work, both users must have crypto phones logged into crypto mode. As with other phones, the signal is encrypted by GSM but it is also encrypted by the cryptographic chip. When the IMSI-catcher performs a man-in-the-middle attack and disables the GSM encryption, the crypto phone encryption remains intact. Therefore, while the signal is still being intercepted, it can no longer be decoded and fake SMS messages can't be sent as the IMSI-catcher does not have the correct code.

Authentication

At the beginning of the call, both users get the same session key by using the hash function. Then the session key becomes a confirm code. The confirm code could be 3 letters or 4 numbers, depending on the phone's manufacturer. In the crypto mode, the user reads the confirm code over the encrypted line to his communication partner and verifies the confirm code his partner reads back. If there is a discrepancy in the confirm code, a man-in-the-middle attack has been detected.

Key Erase

The "session code" that has been established is used only for that specific call. At termination, all the parameters are wiped from memory, and there is no way to reconstruct the code. Intercepted and stored encrypted material can be kept for later analysis, but there is no way to break the code except, possibly, by the time consuming trial-and-error method.

References

↑ Hackers crack open mobile network BBC News Technology
↑ van den Broek, Fabian.Eavesdropping on GSM: state-of-affairs, Radboud University, Nijmegen, Institute for Computing and Information Sciences (iCIS).

External links

Cipher machines

Rotor machines	CCM Enigma M-125 Fialka Hebern HX-63 KL-7 Lacida M-325 Mercury NEMA OMI Portex RED SIGABA SIGCUM Singlet Typex

Mechanical	Bazeries cylinder C-36 C-52 CD-57 Cipher disk HC-9 Kryha Jefferson disk M-94 M-209 Reihenschieber Scytale

Teleprinter	5-UCO BID 770 DUDEK KW-26 KW-37 Lorenz SZ 40/42 Siemens and Halske T52

Secure voice	BID 150 FASCINATOR KY-3 KY-57 KY-58 KY-68 NESTOR OMNI SCIP Sectéra Secure Module SIGSALY STE STU-II STU-III VINSON

Other	JADE KG-84 KL-43 KL-51 Noreen PURPLE GREEN（Japanese：-{グリーン暗号}-） Pinwheel Rockex

Cryptography

History of cryptography Cryptanalysis Outline of cryptography

Symmetric-key algorithm Block cipher Stream cipher Public-key cryptography Cryptographic hash function Message authentication code Random numbers Steganography

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