Narrowband analogue voice scrambler
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KY-65 (KY-65E-1) is a tactical man-portable narrowband
frequency domain voice scrambler,
introduced in 1972
by the USNational Security Agency (NSA)
for use in Vietnam.
It's an analogue system in which the audio spectrum (300-3000 Hz)
is divided into 9 bands of 300 Hz each, which are then swapped and (optionally)
mirrored, under control of the PARKHILL encryption algorithm.
The device is housed in a green metal enclosure that is similar to
that of the PRC-77 radio.
...
KY-65 was introduced in the early 1970s, when the Vietnam War was heating up.
Like all voice scramblers, it is inherently insecure and is therefore
vulnerable to exploitation. Although the NSA was aware of this — the device
was not approved for conversations above Confidential level —
it was deemded better than nothing [4]. It was also assumed that if the
Russians were to exploit it – assuming they were capable and interested–
they 'would have to devote inordinate resources'[4].
Despite their poor security, PARKHILL and compatible devices remained
in use for many years.
It is known that KY-75 was used in the AWACS environment and
for CROSSFOX tactical applications [5].
In 1981, it was even approved by SECAN (NATO) for tactical communication
at all classification levels [6]. At NATO it was regarded as a gap-fill
solution until a definitive secure narrowband voice unit
had been selected for NATO-wide use [6].
In 1989, all PARKHILL devices (KY-65 and KY-75) were replaced by the
KY-65A and KY-75A, which had an improved encryption scheme
and were approved for tactical communication at all classification levels.
These improved systems were is use until well after 2004.
The KY-65 was eventually succeeded from 1994 onward by the much smaller
and more versatile KY-99.
Models
KY-65 (E-1)
This is the inial version of the man-portable model of the device.
Its layout is similar to the PRC-25 and PRC-77 radios, allowing it to
be strapped to a man-portable radio harness.
It can be recognised by a hinged door at the front panel, that covers
the FILL connector. This version was approved for tactical communication at
Confidential level. It was replaced in 1989 by the KY-65A.
KY-75 (E-1)
This is the airborne/shipborne version of the device.
It has different dimensions and a different layout of the front panel,
but is otherwise compatible with the KY-65.
KY-65A
This is a later version of the man-portable KY-65, introduced in 1989,
in which an improved version of the Parkhill encryption algorithm is used.
It is approved for tactical communication at all levels of classification.
This version no longer has a cover over the FILL connector.
It is compatible with the KY-75A.
KY-75A
This is a later version of the airborne/shipborne KY-75, introduced in 1989,
in which a modified version of the Parkhill encryption algorithm is used.
It is compatible with the KY-65A.
KY-65/75 divides the 300-3000 Hz audio spectrum into 9 segments
of 300 Hz each, as illustrated below. Each segment is 300 Hz wide and
can replace any other segment. In addition it may also be mirrored.
The total number of scrambling orders is therefore 18! · 29 =
185,794,560.
Voice band divided into 9 segments of 300 Hz each
In the example below, the nine segments are shown in a scrambled order.
Furthermore, segements 5, 8 and 9 are inverted. The latter means that,
within this band, high tones are replaced by low tones and vice versa.
The scrambling order changes under control of the PARKHILL encryption algorithm.
This is a secret encryption scheme, developed by the NSA.
Same signal but with scrambled frequency bands, some of which are mirrored
Below is a sample of a poor quality recording of KY-65 communication
of the USCPB/DEA. The file was retrieved via the WayBack Machine [7].
It is unknown when it was recorded. In the recording the synchronising AFSK
signal can be heard at the beginning of each conversation.
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Crypto Museum. Created: Friday 20 May 2016. Last changed: Thursday, 21 May 2026 - 08:43 CET.
