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The Private Collection™
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Growing congestion of the airwaves has led to increasing concern for the security of wireless communications. With the widespread availability of RF scanners, anyone from the idle hobbyist to your direct competitor to the most determined criminal can easily record your most sensitive conversations.
First introduced in 1989, the Selectone Private Collection™ has become the industry’s leading solution for secure voice applications over two-way radio systems. With three different levels of security, the Private Collection offers the right amount of protection for nearly any application. With tens of thousands of units in daily service, each backed by a two year factory warranty, you can count on the Private Collection for years of reliable service.
- Three Levels of Security — suitable for most secure speech applications.
- Miniature Size - for easy mounting in most portable and mobile radios.
- High Quality Audio — input and output audio processing filters provide high quality, low distortion audio recovery in encrypted mode.
- Fully Compatible — with nearly all radio systems, including repeaters and trunked systems.
- Over the Air Programming (ST-50 series only) — allows system manager to change code keys or disable lost or stolen units over the air.
- Full Applications Support — with detailed installation instructions for many popular mobile and portable radios.
For any voice encryption application, the level of security required is a function of the sensitivity of the information being transmitted and the sophistication and determination of the persons trying to intercept that information. The Selectone Private Collection features three different levels of security for a wide range of applications: simple inversion, rolling code inversion, and time domain digital encryption. As with all encryption devices, there is a tradeoff between cost, the level of security and the quality of the recovered audio.
- Inversion Scrambling
Simple frequency domain inversion scrambling is the most popular and lowest cost approach to speech security. The cipher process inverts speech frequencies in reference to one of eight possible inversion carriers. The scrambled speech is unintelligible to the casual listener, but the recovered audio is very clear. This type of encryption is suitable for many business and commercial applications to discourage eavesdropping from co-channel users or RF scanners.
- Rolling Code Encryption
The next highest level of encryption is known as frequency domain rolling code. In this method, the cipher process uses a proprietary, microprocessor controlled analog scrambling algorithm with over one trillion available code keys. The encrypted speech is completely unintelligible, but audio processing filters provide high quality recovered audio. While it is possible to "break" an encrypted transmission, to do so requires sophisticated equipment, knowledgeable technical personnel, and considerable time. Therefore, rolling code encryption is suitable for tactical communications typical of most public safety and more critical commercial applications.
- Time Domain Digital Encryption
The highest level of security available for conventional, analog radios is time domain digital encryption. The cipher process uses Digital Signal Processing (DSP) techniques to produce a time domain encryption algorithm. The encryption module digitally records microphone audio for a small time segment. The segment is then subdivided into smaller blocks within the segment. The blocks within each segment are then rearranged in time based on a 72 bit encryption algorithm. The rearranged blocks are then played back for transmission, with playback being in a reverse order. Encrypted audio is completely unintelligible and virtually impossible to break, making time domain encryption suitable for the most sensitive strategic communications. Despite the complexity of the encryption, DSP audio filters provide high quality, low distortion recovered audio.
The ST-20B/C is a miniature, low cost inversion scrambler designed for voice grade communications systems. Applications include commercial shared repeaters and other business and marine radio systems where protection is desired from co-channel users and casual eavesdroppers. The ST-20B/C does not require a license for export.
The unit measures only 0.9"W X 1.5"L X 0.18"H for easy mounting in most portable and mobile radios. Operation is virtually transparent to the user. The Clear/Cipher input, used to enable or disable the cipher mode, is the only user control. A choice of eight field-selectable inversion codes allows compatibility with most commonly used inversion formats.
The standard model for most applications is the ST-20B. The ST-20C is identical but provides a low pass filter in parallel to the normal receive audio path. This path is used for special applications where CTCSS detection must occur after the application point in the host radio. The following Motorola radio models require the use of the ST-20C: M1225, P1225, MT2000 and MT2100.
The ST-25B/C Rolling Code Encryption Module is a miniature, high security voice encryption device especially designed for tactical communications. Up to four user programmable code keys, each selected from over four billion possible keys, may be used to communicate in a secure mode with up to four different groups on the same radio channel. To maintain security, code keys are stored in a non-volatile EEPROM and are never transmitted over the air.
The Clear/Cipher select line is the only user control. Receive mode is automatic, so that clear speech or encrypted speech with the proper code key will be received regardless of the mode selected. Once installed, the ST-25B/C can be enabled or disabled as required. Therefore, it is not necessary to equip an entire fleet with encryption, but only those units where high voice security is required.
Special factory set master code keys may be reserved to provide extra security for special applications. Each master code key group has over 268 million possible code keys. User selectable code keys and other operating parameters are field programmable with a PC using the ST-25PM Product Manager Software.
The standard model for most applications is the ST-25B. The ST-25C is identical but provides a low pass filter in parallel to the normal receive audio path. This path is used for special applications where CTCSS detection must occur after the application point in the host radio. Radios which require the use of the ST-25C are listed above (same as ST-20C).
The ST-50 Series Time Domain Encryption Modules offer the most secure encryption algorithm available for conventional analog radios. Featuring a proprietary DSP design with a 72 bit encryption algorithm, the ST-50 Series provides over one trillion user code keys and one million master code keys. Each radio can be programmed with up to four user-selectable code keys (each selected from 1 trillion possibilities) for secure communication with up to four different groups on the same RF channel. For example, within a police radio system, the captains, lieutenants, and sergeants could each have their own private group code key, as well as a common code key for all three groups.
Operation of the ST-50 Series is almost transparent to the user. The user selects any one of four user code keys, then enables or disables the cipher (encrypted) mode. Once enabled, all subsequent transmissions will be ciphered using the selected code key. Ciphered reception is automatic, so that other units transmitting with the selected code key will be deciphered. Clear (un-ciphered) transmissions will be received automatically.
Because synchronization data is sent continuously, the ST-50 Series also offers "late join" capability. This feature enables the user to join a secured communication already in progress or to re-join a secured communication if the radio signal is momentarily lost.
In addition to high security, the ST-50 Series offers Over the Air Programming (OtAP) which allows the system administrator to change code keys over the air after initial setup. The OtAP feature may also be used to remotely "stun" or "kill" a lost or stolen radio without having to re-program an entire fleet. (Note: use of the OtAP feature requires the ST-955 OtAP Modem Kit.)
The ST-50 Series consists of three different models: ST-52, ST-51, and ST-50.
- The ST-52 divides microphone audio into small time segments in the range of 100 mS to 600 mS. These segments are further divided into blocks within each segment. The blocks are then re-arranged in time based on a 72 bit encryption algorithm and transmitted. The reverse of the process is applied at the receiving point. The ST-52 may be exported without a license.
- The ST-51 increases the level of security by increasing the number of blocks within a segment and continuously changing (rolling) the encryption sequence for each segment.
- The ST-50 further increases the level of security by further increasing the number of blocks within a segment, while rolling the encryption sequence.
Note: The ST-50 and ST-51 require an export license - see Export Restrictions.
The security level of an encryption device is a function of the time and difficulty required to decipher the transmission. Simple speech inversion provides protection against the casual listener, but any knowledgeable hacker can break it easily in real time. To break tactical level encryption requires considerably more time and equipment, so that by the time someone is able to decode the transmission, the content of the communication no longer has any value. On the other hand, if the communication has strategic value, a time domain algorithm will provide much greater long term protection.
The chart below illustrates the relative security of inversion scrambling, rolling code encryption, and time domain encryption. Let’s assume that the complexity required to break an encryption device (in terms of time and equipment) is represented by a line on a wall, with the tallest line being the most secure. If this were the case, simple inversion scrambling (ST-20B/C) would be represented by a line one inch high. Rolling code encryption (ST-25B/C) would be represented by a line one mile high. The lowest level of Time Domain encryption (ST-52) would be a line 50,000 miles high. The mid-level Time Domain encryption (ST-51) would be a line from the earth to the moon. And finally, the most secure Time Domain encryption (ST-50) would be represented by a line from the earth to the sun and back!
To simplify installation, we offer application specific versions of our model ST-20 and ST-25 for certain radios. These models include installation kits with special components and wiring diagrams for installation in the host radios.
- ST-20/25BK - Kenwood TK-790/890
- ST-20/25BGP - Motorola GP300/350
Since most radios do not provide any connection points for a scrambler, the installation of any secure speech equipment in a two-way radio is often a difficult task. Installation requires a minimum of eight external connections in the radio: power, ground, transmit audio input and output, receive audio input and output, PTT input, and clear/ciphered input. The most critical connections are the inputs and outputs for transmit and receive audio. Improper installation of these connections can result in distorted audio and the loss of high or low frequency voice components.
To assist you with the installation of our encryption modules, we offer a library of Application Notes with recommended connection points, mounting and programming instructions for many models of two-way radios. If we do not have an Application Note for the radio and encryption model you are considering, please contact our Technical Support Department before attempting installation.
The export of most encryption devices is controlled by the United States Department of Commerce, Bureau of Export Administration. Shipments of the ST-25B/C, ST-50, and ST-51 outside of the United States or Canada must identify the end user of the equipment, which will be reported to the Department of Commerce. .
Customers in the United States who purchase encryption equipment for re-export to another country (except Canada) must apply to the Department of Commerce for an export license in their own name. Some countries are restricted from export – contact factory for details.
Note: The ST-20B/C Inversion Scrambler and the ST-52 Time Domain Encryption Module DO NOT require an export license.
The ST-955 Modem is required for Over the Air Programming (OtAP) of any of the ST-50 Series Time Domain Encryption Modules. The ST-955 connects to a PC running Selectone ST-50PM Product Manger™ software via a female DB9 (RS232) serial connection. The ST-955 also connects to the host radio or service monitor via a male DB9 connector. All operation is under control of the Product Manger software.
After initial setup, the user code keys of the ST-50/51/52 can be re-programmed remotely over the air with the ST-955 Modem. The ST-955 can also be used to remotely "stun" or "kill" a lost or stolen radio.
Like most Selectone products, the ST-25B/C and the ST-50/51/52 are PC programmable using Selectone Product Manager software. The ST-25PM Product Manager is required to program the ST-25B/C, while the ST-50PM is required to program the ST-50 Series. These programs may be ordered from the factory or downloaded from the Selectone Website by clicking here.
A ST-954 Programming Kit is required for programming the code keys and other operating parameters of the ST-25B/C and ST-50 Series. (Note: The ST-20B/C is not PC programmable and therefore does not require a programming kit.) The ST-954 kit consists of three items: a ST-954B Programming Adapter which interfaces between a PC and the Selectone encryption module; a 6’ RS-232C serial cable assembly; and a DB9 to DB25 adapter plug. The ST-954 kit may be used to program most Selectone products.
For customers who already have a serial cable, the ST-954B Programming Adapter may be purchased separately or constructed from a circuit schematic available from the Selectone Website by clicking here.
OPERATING SPECIFICATIONS
SPECIFICATION ST-20B/C ST-25B/C ST-50 SERIES Encryption Frequency Inversion 24 bit algorithm with 32 bit code key 72 bit algorithm with 72 bit code key Operating Voltage 5.2 Vdc to 16.3 Vdc 5.2 Vdc to 16.3 Vdc 5.2 Vdc to 16.3 Vdc Operating Current <8mAdc <8mAdc Clear Rx & Standby
n/a n/a <10mAdc Ciphered Rx or Tx
n/a n/a <60mAdc Available Carrier Frequencies 8 n/a n/a Available User Code Keys n/a Greater than 4 billion 1.15 x 1018 (1012 or 1 Trillion) Cipher Algorithm n/a Real Time Frequency Domain Time Domain Synchronization n/a Initial & Maintenance Initial & Maintenance (supports late join) Usable Audio Level Rx and Tx 25 mV p-p to 2.0 V p-p 25 mV p-p to 2.0 V p-p 25 mV p-p to 2.5 V p-p Input to Output Gain <±1dB <±1dB <±1dB Frequency Response (ST-20B)
300Hz to 2600Hz
(ST-20C)
67 to 250 No cipher
300Hz to 2600Hz(ST-25B)
300Hz to 2600Hz
(ST-25C)
67 to 250 No cipher
300Hz to 2600Hz300Hz to 3000Hx Temperature Range -30°C to +60°C -30°C to +60°C -30°C to +60°C Interface 18" flying leads terminated in a 13 pin low profile connector 18" flying leads terminated in a 13 pin low profile connector 18" flying leads terminated in a 13 pin low profile connector Size 0.90"W x 1.5"L x 0.18" H
(22.8mm x 38.1mm x 4.6mm)0.90"W x 1.5"L x 0.18" H
(22.8mm x 38.1mm x 4.6mm)0.85"W x 1.5"L x 0.25" H
(21.6mm x 38.1mm x 6.3mm)Specifications and descriptions subject to change without notice
© 1999, Communications Specialists, Inc. All rights reserved.
Last updated March 31, 2003