Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02541860 2000-04-14
METHODS AND APPARATUS FOR TRANSMITTING, RECEIVING, AND
PROCESSING SECURE VOICE OVER INTERNET PROTOCOL
I. BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to a method and apparatus for processing voice
data for
transmission and receipt over a network. More particularly, the invention
relates to methods
and apparatus for processing of secure voice communications for transmission
and receipt
over a network.
B. Description of the Related Art
The advent of digital networks has expanded the possibilities for the exchange
of
information. In panicular, the speed of communications over these networks has
developed
dramatically. Most recently, the speed of digital networks has almost doubled
even' three
years. Due to the new capabilities resulting from the improvements in speed,
the
transmission not only of data but also of voice and multimedia has become
feasible.
However. the security for these types of communications has not matched the
improvements
in speed.
Indeed, with the technological sophistication of digital networks, many users
have
begun to utilize digital networks for voice communications. Of course. as with
any form of
voice communications. confidentiality is a primary concern. Specifically,
because voice
communications entail important commercial and governmental information. there
is an
obvious need for confidentiality and security. In addition, the need for
secure voice
communications will also include communications over a wire line as well as
communications over digital networks. Moreover. as digital networks are used
more and
more for multimedia applications, the same concerns of confidentiality and
security will
become relevant outside of the confines of voice communications.
With conventional systems and methods for secure voice communications over
wire
lines, there are a limited number of types of secure telephone equipment. such
as secure
telephone unit, 3rd generation (STLT-III) equipment and secure terminal
equipment (STE).
However. STU-III uses obsolete synchronous analog techniques. and STE requires
an ISDN
connection. For these reasons. these systems axe generally considered
inadequate for secure
voice communications.
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With the present systems and methods for secure communications over digital
networks. such as. for example, the Internet. neither STU-III nor STE is
compatible with
Internet-based networks. In fact. the only known means of transmitting and
receit~in_ secure
voice communications using an Internet protocol is the PGP-Fone. The PGP-Fone
is
distributed over the Internet and utilizes the PRETTY GOOD PRIVACY (PGP)
encryption
technique. However, the PGP-Fone does not support narrowband and similar
bandwidth-
limited connections. In addition, the PGP-Fone is incompatible with government-
standardized voice coding and cryptographic techniques. such as mixed
excitation linear
prediction (MELP) for voice coding and SHIPJACK for encryption. As a result,
the PGP-
Fone does not entail the technical sophistication necessary for adequate
secure voice
communications over a digital network, such as the Internet.
Due to the absence of a system or method of transmitting, receiving, and
processing
voice data in a secure manner over the Internet. there is a general need for
such a system and
method. In addition, there is also a need for such a secure system and method
for the highly
important voice communications of business and government. including those
that require an
Internet connection.
II. SUMMARY OF THE INVENTION
Methods and apparatus consistent with the present invention overcome the
shortcomings of the conventional systems by processing secure voice for
transmission and
receipt over a network.
In accordance with the purposes of the invention, as embodied and broadly
described
herein, one aspect of the invention includes a method consistent with the
present invention of
transmitting sound. This method comprises receiving an analog signal
representing sound,
converting the analog signal into digital information, translating the digital
information into a
data frame using a linear prediction technique, encrypting the data frame into
a ciphertext
frame. forming a secure voice frame from the ciphertext frame, and
transmitting the secure
voice frame.
In another aspect. the invention includes a method for receiving sound.
comprising
the steps of receiving a secure voice frame. removing a header from the secure
voice frame to
obtain a ciphertext frame, decn~pting the ciphertext frame into a data frame.
translating the
data frame into digital information using a linear prediction technique.
converting the digital
CA 02541860 2000-04-14
information into an analog signal representing sound, and outputting the
sound.
in vet another aspect. the invention includes a method for transmitting and
receiving
speech. comprising the steps of receiving an analog signal representing
speech. converting
the analog signal into digital information. translating the digital
information into a data frame
using a linear prediction technique. storing the data frame in a first
transmitter buffer.
encrypting the data frame into a ciphertext frame using a codebook encryption
algorithm,
storing the ciphertext frame in a second transmitter buffer, forming a secure
voice frame from
the ciphertext frame. transmitting the secure voice frame over a network,
receiving the secure
voice frame over a network. removing the header from the secure voice frame to
obtain the
ciphertext frame, storing the ciphertext frame in a first receiver buffer.
decrypting the
ciphertext frame into a data frame using a codebook decryption algorithm.
storing the data
frame in a second receiver buffer, translating the data frame into digital
information using a
linear prediction technique. converting the digital information into an analog
signal
representing speech, and outputting the speech.
Additional aspects of the invention are disclosed and defined by the appended
claims.
it is to be understood that both the foregoing general description and the
following detailed
description are exemplary and explanatory and are intended to provide further
explanation of
the invention as claimed.
III. BRIEF DESCRIPTION OF THE DRAVS'INGS
The accompanying drawings are included to provide a further understanding of
the
invention. or incorporated in and constitute a part of this specification.
illustrate preferred
embodiments of the invention, and. together with the description, serve to
explain the
principles of the invention.
In the drawings,
Figure 1 is a block diagram of a secure voice over Internet protocol system
consistent
with the principles of the present invention;
Figure 2 is a block diagram of a secure voice over Internet protocol encoder
system
and a secure voice over Internet protocol decoder system in accordance with
one embodiment
of the present invention:
Figure .i is a flow chart of the operations of a secure voice over Internet
protocol
encoding system in accordance with one embodiment of the invention;
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-r
Figure ~4 is a flow chart of the operations of a framing scheme in accordance
with the
embodiment of the invention:
Figure ~ is a block diagram of a framing scheme in accordance with the
embodiment
of the invention: and
Figure 6 is an illustration of a secure voice frame. in accordance with one
embodiment of the present invention.
IV. DETAILED DESCRIPTION
A. Introduction
A system consistent with the principles of the present invention as disclosed
herein
provides for processing secure voice communications for transmission and
receipt over a
network. The methodology used by the disclosed system conforms to standards
for voice
coding and cryptography. Accordingly, the system avoids the shortcomings of
the present
systems and methodologies, which are incompatible with government-standardized
voice
coding and cryptographic techniques. For example, for voice coding. the system
utilizes
mixed excitation linear prediction (MELP), although other coding techniques
may be used,
such as. for example, code excited linear prediction (CELP). Furthermore. for
cryptography.
the system utilizes SKIPJACK, which is a standard. but again, other encn~ption
schemes may
be used, such as, for example, the Government Tvpe 1 requirements known to
those skilled in
the art. 'L'ith the disclosed system. and as otherv~.~ise described herein,
the transmission and
receipt of secure voice communications over a network is made possible.
Further. with the
disclosed system, secure voice communications may occur over narrowband and
other
bandwidth-limited connections. This capability ensures compatibility with
future
narrowband digital terminal (FNBDT) equipment. including CONDOR equipment.
Moreover. the system is also compatible with both wireline and wireless
networks.
Accordingly, due to this scope of compatibility. the system is much less
expensive than
current systems and methods for secure voice communications.
B. System
Figure 1 illustrates a block diagram of a secure voice over Internet protocol
system
according to the present invention. System 100 comprises a voice source 110. a
secure voice
device 1?0. a network 130, such as. for e~cample. the Internet. a secure voice
device 1-10. aid
a voice destination 1~0. Voice source 110 and voice destination 1~0 may both
serve as the
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source and destination of a voice input or voice output. Secure voice device
120 and secure
voice device 140 similarly process voice information for transmission and
receipt via
network 130. Accordingly, secure voice 120 and secure voice 1=10 contain both
a secure
voice encoder and secure voice decoder. Notably, although the description of
the present
invention encompasses voice communications, systems consistent with the
invention may
also operate with data or other objects over any form of network. Indeed, one
likely
alternative use of the present invention is for multimedia.
Figure 2 illustrates a block diagram of a secure voice over Internet protocol
encoder
system and a secure voice over Internet protocol decoder system. in accordance
with one
embodiment of the present invention: In this embodiment. encoder/decoder
system 200
comprises voice source 1 I0. encoder 210. Internet 2~0. decoder 260, and voice
destination
1 ~0. Encoder 210 comprises analog-to-digital converter 2I ~, voice coder 220.
construct
voice frame device 225, encryption device 230, assemble secure voice frame
device 23~, and
transmit secure voice frame device 240. Decoder 260 includes receive secure
voice frame
device 26~, disassemble secure voice frame device 270, decryption device 27~,
deconstruct
voice frame device 280, voice decoder 285, and digital-to-ana.iog converter
290. Notably,
both encoder 210 and decoder 260 comprise the same basic components. Thus,
either
encoder 210, decoder 260, or both. may be implemented at any standard
terminal, such as. for
example. a Windows-based personal computer.
As shown in Figure 2, voice source 110 provides a voice input for encoder 210.
Encoder 210 then processes the voice input to create a secure voice frame for
transmission
over Internet 2~0. In one embodiment. encoder 210 may negotiate a session key
before
processing the voice input for transmission. A session key allows the
participating devices to
communicate using a specified type of encryption. In one implementation of
this
embodiment, encoder 210 contains pre-placed keys, such as, for example, pre-
placed
SKIPJACK keys. In another implementation of this embodiment, the negotiation
of the
session key may include the use of the key exchange algorithm (KEA). KEA is a
1024-bit
key exchange algorithm. Of course. other implementations of this embodiment
may also be
used to neeotiate the session key.
As also shown in Figure 2, once encoder 210 receives the voice input, analoe-
to-
diQital converter 21~ converts the voice information tiom an analog sicnal to
digital
information. Next. voice coder 220 compresses the digital information
according to a
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compression technique. In one embodiment. voice coder ??0 utilizes mixed
excitation linear
prediction (MIELP) as the compression technique. MELP is a standard
compression
technique. Other standard compression techniques may also be used. such as the
code
excited linear prediction (CELP) technique. Essentially, any compression
technique used for
voice or data would represent a valid coding substitute. In one
implementation, voice coder
220 is a digital signal processor (DSP) with MELP software. However, a DSP is
not
necessary. In another implementation. voice coder 220 is entirely software. In
such a
software implementation. voice coding could be entirely performed by a
standard personal
computer. Indeed, in a personal computer. a standard sound card (such as, for
example, a
Sound BlasterTM card) could even be used to facilitate voice coding.
After voice coder 220. encoder 210 transfers the compressed digital
information from
voice coder 220 to construct voice frame device 22~. Construct voice frame
device 22~
assembles the compressed digital information into a voice frame. Next, encoder
210 encrypts
the voice frame. using encryption device 230. In one embodiment. encryption
device 230
may include either a hardware implementation or a software implementation. A
hardware
implementation may include. for example, a commercially available Fortezza PC
card. A
software implementation may include, for example. a software program such as.
for example.
Spyrus Software Fortezza. One example of such a software routine is SKIPJACK.
SKIPJ_ACK is an 80-bit encryption algorithm that is not extensible to higher
key lengths.
Notably, in a software implementation, encryption could be performed by a
standard personal
computer.
Encryption device 230 changes the voice frame to a cipherteart frame by the
addition
of a ciphertext header. Once the ciphertext voice frame is created. encoder
210 then
assembles a secure voice frame in assemble secure voice frame device 23~. In
one
embodiment, encoder 210 assembles a secure voice frame by adding a sequence
number and
frame check sequence to the ciphertext voice frame obtained from encryption
device 230.
Finally, encoder 210 transmits the secure voice frame according to transmit
secure voice
frame device 240 over Internet 250. In one embodiment, transmit secure voice
frame device
340 prepares the secure voice frame for transmission by adding padding to the
secure voice
frame obtained from secure voice frame device 240. Padding is the addition of
one or more
additional bits to the secure voice frame. In one implementation. the secure
voice frame is
then transmitted via user datagram protocol. Internet protocol (UDP/IP). which
is a
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connectionless. best-effon communications method for exchaneinc messases
between
computers in a network. UDP is a connectionless protocol. as contrasted with
the "TLP!IP
protocol. LTDP/IP is an advantageous transmission protocol because IP
datagrams can tal;e
different paths tllrouah the network. The use of UDP/IP is also advantageous
because the
protocol may be implemented for use with F~BDT equipment.
After encoder ? 10 constructs the secure voice frame, and after transmit
secure voice
frame device 240 prepares the secure voice frame for transmission, encoder ?
10 transmits the
secure voice frame over Internet 250. Decoder 260 receives the secure voice
frame from
encoder ? 10 via Internet 250. Decoder ?60 then utilizes a decoding process
similar to the
encoding process utilized by encoder ? I O to translate the secure voice frame
to a voice
output. Decoder 260 receives the secure voice frame at receive secure voice
frame device
X65. If encoder 210 transmits the secure voice frame using UDP/IP. decoder 260
also utilizes
UDP/IP to receive the secure voice frame at secure voice frame device 265.
Notably. if
UDP/IP is used. a static or dynamic fitter buffer is utilized at secure voice
frame device 26~
to allow for each secure voice frame to be rearranged upon receipt, in order
to account for
any transit and buffering delays in the network. This is necessary due to the
nature of
UDP/IP. Of course, other implementations may use other protocols. and a fitter
buffer would
be optional in those implementations. For example. TCP/IP could always be used
as an
alternative. and the real time protocol (RTP) is one of several other possible
protocol
supplements for UDP/IP.
Once decoder 260 receives the secure voice frame at secure voice frame device
?6~.
decoder 260 disassembles the secure voice frame according to disassemble
secure voice
frame device 270. In one embodiment. disassembly of the secure voice frame
involves
removal of the sequence number and frame check sequence: If padding was used
for
transmission, then the padding is also removed from the secure voice frame.
Following this
disassembly of the secure voice frame. decoder 260 then decrypts the
cipherte~t voice frame
using decr<~ption device 275. As in encoder ? 10. in one embodiment.
decryption device '_'75
may include either a hardware implementatior. or a software implementation.
Follomin~
decryption of the ciphertext voice frame. decoder 260 then deconstructs the
voice frame
according to deconstruct voice frame device 280. The deconstruction of the
voice frame
includes voice decoder 255. According to one embodiment. voice decoder ?85
utilizes
VIELP coding to decompress the compressed digital information into
uncompressed digital
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information. Following the decompression, decoder 260 finally converts the
digital
information into an analog signal with digital-to-analog converter'_'90. Once
the digital
information is converted into an analog signal, decoder 260 may then output
the voice output
to voice destination 1~0.
Notably, Figure 2 depicts a secure voice over Internet protocol encoder and a
secure
voice over Internet protocol decoder system, both of which operate over an
Internet 2~ 0.
Further. as stated above, one embodiment of these systems includes an
implementation that
takes place on a standard personal computer over a network. Yet. these systems
may aiso
operate via a traditional public-switch telephone network.
Figure 3 is a flow chart of the operations of a secure voice over Internet
protocol
encoding system in accordance with one embodiment of the invention. Figure 3
depicts how
analog voice data is taken from a voice transmission and convened to a secure
voice frame
nor transmission according to an embodiment of the invention. As shown in
Figure 3. a block
of voice information 30~ is taken from an analog stream of voice data 310 for
encoding.
During encoding, such as during the process for the system in encoder 210 of
Figure 2.
analog voice information is converted into digital information, i.e., a
digital frame of voice
data. .Create digital frame of voice data 315 corresponds to the operation of
analog-to-digital
converter 21 ~ in Figure 2. Next, digital frame of voice data 31 ~ is
converted into a coded
voice frame. Create coded voice frame 320 corresponds to the operations of
voice coder 220
and construct voice frame device 225 in Figure 2. Create coded voice frame 320
includes
both compression of the digital information and placement of that digital
information into a
name, yielding a coded voice frame. Next, the coded voice frame is encrypted
to create a
ciphertext voice frame. As shown in Figure 3, create ciphertext header 322 is
used to add a
header to the coded voice frame to create the ciphertext voice frame. Create
ciphertext
header 322 may optionally occur while the coded voice frame is played in
buffer coded voice
frame 324. Create ciphertext voice frame 330 corresponds to the operation of
encryption
device 230 in Figure 2. Next, the ciphertext voice frame is converted into a
secure voice
frame. As shown in Figure 3. create secure voice header 332 is used to add
another header to
the ciphertext voice frame to create the secure voice frame. Create secure
voice header 332
play optionally occur while the ciphertext voice frame is placed in buffer
ciphertext voice
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9
frame 334. Create secure voice frame 33~ corresponds to the operation of
assemble secure
voice frame device ?35 in Figure 2. Next. the secure voice frame is prepared
for
transmission. As described above, in one embodiment, a secure voice frame is
prepared for
transmission by adding padding to the secure voice frame. Prepare secure voice
frame for
transmission 340 corresponds to the operation of transmit secure voice frame
device 240 in
Figure 2.
C. Illustration of Framing
Figure 4 is a flow chart of the operations of a framing scheme in accordance
with the
embodiment of the invention. However, Figure 4 illustrates only one of many
possible
framing schemes according to this embodiment. According to this scheme, a
block of data
40~ is taken from an analog data stream 410 by sampling the analog speech and
preparing
samples. or blocks of data. According to the process and system described
above in Figure 3.
a block of data 405 is then converted into a digital voice frame 415. Next,
digital voice
frame 415 is converted into a coded voice frame 420. A ciphertext voice frame
430 is then
created by the addition of a ciphertext header 422. The creation of ciphertext
voice frame
430 may optionally include buffer 424, which may hold coded voice frame 420
during the
creation of ciphertext header 422. Next, a secure voice frame 435 is created
by the addition
of a secure voice header 432 to ciphertext voice frame 430. The creation of
secure voice
frame 435 may optionally include buffer 434, which holds ciphertext voice
frame 430 durine
the creation of secure voice header 432. Finally, secure voice frame 435 is
prepared for
transmission as a transmission frame 440. Transmission frame 440 includes the
addition of
padding to secure voice frame 435, which results in the creation of
transmission frame 440.
Figure 5 is a block diagram used to explain the technique described above in
connection with Figure 4. However, Figure 5 illustrates only one of many
possible ways of
framing a secure voice frame. Indeed, other framing implementations (and other
header
arrangements) would be compatible with systems consistent with the invention.
The framing
example in Figure 5, however, presents one of the more efficient framing
implementations.
According the framing example in Figure 5, a block of data 505 is taken from
an
analog data stream ~ 10 for conversion into a digital voice frame. Block of
data 505 contains
a sample of an analog signal from analog data stream 510. Digital voice frame
515 contains
a frame of digital information, following conversion of the analog signal from
block of data
505 into digital information. Digital voice frame 515 comprises an unspecified
number of
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1U
bits. as digital voice frame ~ I 5 simply represents the conversion of an
anaio~ signal into a
digital format. Coded voice frame ~~G comprises a frame of coded voice
information.
followine conversion of digital voice frame 51~ to a coded voice frame. In one
embodiment.
using \~TELP, coded voice frame 5?0 consists of 54 bits of information,
representing 2?.5
milliseconds of actual speech. Following the creation of coded voice frame
520, a ciphertext
header 5?2 is created. which will be appended to coded voice frame 520. In one
embodiment, using SKIPJACh, ciphertext header 522 comprises 1 I bits. In this
embodiment. the 1 I-bit ciphertext header consists of a frame sequence
counter. Notably.
coed voice frame 520 may optionally be held in buffer 524, pending creation of
ciphertext
header 522. Thus, coded voice frame 520 in buffer 524 may be joined with
ciphertext header
522 to create cipherte~t voice frame X30.
Following creation of ciphertext voice frame X30, secure voice header 532 is
created_
which will be appended to ciphertext voice frame 530. In one embodiment.
secure voice
header X32 comprises 1 ~ bits. In this embodiment, 11 of the 1 s bits
represent a frame
sequence number and 4 of the I5 bits represent a check sum. Notably,
ciphertext voice frame
530 may optionally be held in buffer X34, pending creation of secure voice
header X32. Thus.
ciphertext voice frame 530 in buffer 534 may be joined with secure voice
header 532 to
create secure voice frame ~3~.
Following creation of secure voice frame 535, transmission frame X40 may be
created. Transmission frame 540 contains some form of padding. In one
embodiment.
transmission frame 440 contains a 1-bit pad. Accordingly, as shown in Figure
5,
transmission frame 540 comprises secure voice frame 535 plus padding 542.
Figure 6 is an illustration of a secure voice header with padding, in
accordance with
one embodiment of the Dresent invention. In Fieure ~, transmission frame X42
depicts a
preferred embodiment of a transmission frame. As also shown in Figure ~,
transmission
frame 540 comprises a 54-bit coded voice frame 520. an 11-bit ciphertext
header 522. a 15-
bit secure voice header X32. and a 1-bit padding 542. Figure 6 specifically
illustrates secure
voice header 532 and padding 542. As shown in Figure 6, secure voice header
532 is a l ~-bit
header. comprising a frame sequence number and a check sum. In one embodiment.
as in
Figure 6. the frame sequence number is the 11-bit ciphertext header. Also in
this
embodiment, the 4-bit check sum is created by 4-bit Hamming encoding, using
Hamming
encoding on the 11-bit frame sequence number. Also as shown in Figure 6,
padding 542
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includes padding that is added to secure voice header ~3?. In one embodiment.
as in Figure
6, padding ~=12 is a I-bit pad. v~,~hich ensures octet-adjustment. In one
implementation. tile
padding is a reserved bit and is set to 0. As shown in Figure b. the padding
is the most
significant bit of the transmission frame.
V. CONCLUSION
Systems consistent with the present invention overcome the disadvantages of
the
traditional mechanisms for processing secure voice communications over a
network.
Specifically, by combining voice coding with encryption as described above,
the systems of
the invention as disclosed herein provide for secure voice communications over
a network,
which overcome the shortcomings of the present systems and methods. Secure
voice
communications as disclosed herein occur using systems that conform to federal
standards
for voice coding and cryptography. applicable for both commercial and
governmental
applications (including unclassified governmental applications). For
commercial
applications, one embodiment of such systems may entail software-implemented
cryptography. For governmental applications, such as classified governmental
applications.
another embodiment of such systems may entail hardware-implemented encryption.
Other
embodiments are also possible, such as, for example, mixed software- and
hardware-
implemented voice coding andlor encryption. Significantly, at least one
embodiment of these
systems would be compatible with narrowband and other limited-bandwidth
connections.
As described above. therefore. it will be apparent to those skilled in the art
that
various modifications and variations can be made in the methods and apparatus
of the present
invention without departing from the spirit and scope of the invention. Thus.
it is intended
that the present invention cover the modifications and variations of this
invention, provided
they come within the scope of the appended claims and their equivalents. In
this context,
equivalents mean each and every implementation for carrying out the functions
recited in the
claims, even if not explicitly described herein.
