US5060265A
Expired / Lapsed
US
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Method of protecting a linear feedback shift register (LFSR) output signal
Assignee: Motorola Solutions Inc
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Filing: 1990-07-23
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Granted: 1991-10-22
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Expires: 2010-07-23
Abstract
Abstract The present invention discloses a method of protecting a pseudorandom (PN) signal generated by a linear Feedback Shift Register (LFSR) from cryptographic attack. This is accomplished by first receiving a PN output signal generated by an LFSR, or by clocking an LFSR to produce a PN output signal. Thereafter, non-linearity is deterministically introduced into the PN signal to produce a deterministic bit pattern. According to the suggested embodiments, the introduction of non-linearity is accomplished by altering at least one bit of the PN signal sequence. Next, the deterministic bit pattern is substituted in place of the LFSR PN signal, thereby protecting the PN signal from cryptographic attack.
Inventors
- 👤 Louis D. Finkelstein
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 14:19
CPC Classifications
H; H03; H03K; H03K3/00; H03K3/84; H04; H04L; H04L9/00; H04L9/002; H04L9/06; H04L9/065; H04L9/0656; H04L9/0662; H04L9/0668
Claims Analysis
Total Claims: 25
Claim 1
Independent Claim
55 words
A method of protecting a pseudorandom (PN) signal generated by a Linear Feedback Shift Register (LFSR) from cryptographic attack comprising the steps of: deterministically introducing non-linearity into the PN signal to produce a deterministic bit pattern; and substituting the deterministic bit pattern for the PN signal, whereby the PN signal is protected from cryptographic attack.
Claim 2
Independent Claim
55 words
A method of protecting a pseudorandom (PN) signal generated by a Linear Feedback Shift Register (LFSR) from cryptographic attack comprising the steps of: deterministically introducing non-linearity into the PN signal to produce a deterministic bit pattern; and substituting the deterministic bit pattern for the PN signal, whereby the PN signal is protected from cryptographic attack.
Claim 3
Dependent Claim
30 words
The method of claim 1 wherein the step of deterministically introducing non-linearity into the PN signal further comprises the step of: altering at least one bit of the PN signal.
Claim 4
Dependent Claim
74 words
The method of claim 2 wherein the step of altering at least one bit of the PN signal further includes the steps of: adding at least a portion of the LFSR content to at least a portion of the register content to obtain an address; fetching a look-up table entry from a look-up table at a location corresponding to the address; and comparing the look-up table entry to a reference to determine a match.
Claim 5
Dependent Claim
14 words
The method of claim 3 wherein the step of adding is a modulo-two addition.
Claim 6
Dependent Claim
69 words
The method of claim 2 wherein the step of altering at least one bit of the PN signal is an alteration selected from the group of alterations consisting of: masking the state of at least one bit of the PN signal; ignoring the state of at least one bit of the PN signal; and repositioning the location of at least one bit of the PN signal, upon a comparison.
Claim 7
Dependent Claim
42 words
The method of claim 2 wherein the reference is a bit pattern selected from the group of bit patterns consisting of: LFSR contents; flip flop contents; latch contents; shift register contents; working register contents; memory device address contents; and software variable contents.
Claim 8
Independent Claim
71 words
A method Of protecting a pseudorandom (PN) signal generated by a Linear Feedback Shift Register (LFSR) from cryptographic attack comprising the steps of: clocking an LFSR to produce a PN signal; altering at least one bit of the PN signal to produce a deterministic bit pattern; and substituting the deterministic bit pattern for the PN signal, whereby non-linearity is deterministically introduced into the PN signal to protect it from cryptographic attack.
Claim 9
Independent Claim
71 words
A method Of protecting a pseudorandom (PN) signal generated by a Linear Feedback Shift Register (LFSR) from cryptographic attack comprising the steps of: clocking an LFSR to produce a PN signal; altering at least one bit of the PN signal to produce a deterministic bit pattern; and substituting the deterministic bit pattern for the PN signal, whereby non-linearity is deterministically introduced into the PN signal to protect it from cryptographic attack.
Claim 10
Dependent Claim
17 words
The method of claim 7 further comprising the step of: initializing the LFSR to an initial state.
Claim 11
Dependent Claim
33 words
The method of claim 7 wherein an LFSR is a medium selected from the group of storage media consisting of: flip flops; latches; shift registers; working registers; memory device addresses; and software variables.
Claim 12
Dependent Claim
64 words
The method of claim 7 wherein the step of altering at least one bit of the PN signal further includes the steps of: adding the LFSR content to a register content to obtain an address; fetching a look-up table entry from a look-up table at a location corresponding to the address; and comparing the look-up table entry to a reference to determine a match.
Claim 13
Dependent Claim
14 words
The method of claim 10 wherein the step of adding is a modulo-two addition.
Claim 14
Dependent Claim
69 words
The method of claim 10 wherein the step of altering at least one bit of the PN signal is an alteration selected from the group of alterations consisting of: masking the state of at least one bit of the PN signal; ignoring the state of at least one bit of the PN signal; and repositioning the location of at least one bit of the PN signal, upon a comparison.
Claim 15
Dependent Claim
42 words
The method of claim 10 wherein the reference is a bit pattern selected from the group of bit patterns consisting of: LFSR contents; flip flop contents; latch contents; shift register contents; working register contents; memory device address contents; and software variable contents.
Claim 16
Independent Claim
118 words
A method of protecting the pseudorandom (PN) sequence generated by a Linear Feedback Shift Register(LFSR) from cryptographic attack comprising the steps of: clocking an LFSR to produce an PN sequence; adding at least a portion of the LFSR's content to a register content to obtain an address; fetching a look-up table entry from a look-up table at a location corresponding to the address; comparing the look-up table entry to a reference to determine a match; altering at least one bit of the PN sequence upon a comparison, to produce a deterministic bit pattern; and substituting the deterministic bit pattern for the PN sequence, whereby non-linearity is deterministically introduced into the PN signal to protect it from cryptographic attack.
Claim 17
Independent Claim
118 words
A method of protecting the pseudorandom (PN) sequence generated by a Linear Feedback Shift Register(LFSR) from cryptographic attack comprising the steps of: clocking an LFSR to produce an PN sequence; adding at least a portion of the LFSR's content to a register content to obtain an address; fetching a look-up table entry from a look-up table at a location corresponding to the address; comparing the look-up table entry to a reference to determine a match; altering at least one bit of the PN sequence upon a comparison, to produce a deterministic bit pattern; and substituting the deterministic bit pattern for the PN sequence, whereby non-linearity is deterministically introduced into the PN signal to protect it from cryptographic attack.
Claim 18
Dependent Claim
33 words
The method of claim 14 wherein an LFSR is a medium selected from the group of storage media consisting of: flip flops; latches; shift registers; working registers; memory device addresses; and software variables.
Claim 19
Dependent Claim
14 words
The method of claim 14 wherein the step of adding is a modulo-two addition.
Claim 20
Dependent Claim
66 words
The method of claim 14 wherein the step of altering at least one bit of the PN sequence is a alteration selected from the group of alterations consisting of: masking the state of at least one bit of the PN sequence; ignoring the state of at least one bit of the PN sequence; and repositioning the location of at least one bit of the PN sequence.
Claim 21
Dependent Claim
42 words
The method of claim 14 wherein the reference is a bit pattern selected from the group of bit patterns consisting of: LFSR contents; flip flop contents; latch contents; shift register contents; working register contents; memory device address contents; and software variable contents;
Claim 22
Independent Claim
66 words
An apparatus for protecting the pseudorandom (PN) signal generated by a Linear Feedback Shift Register (LFSR) from cryptographic attack comprising: means for deterministically introducing non-linearity into a PN signal to produce a deterministic bit pattern; and substituting means, coupled to the means for deterministically introducing non-linearity, for substituting the the deterministic bit pattern for the PN signal, whereby the PN signal is protected from cryptographic attack.
Claim 23
Independent Claim
66 words
An apparatus for protecting the pseudorandom (PN) signal generated by a Linear Feedback Shift Register (LFSR) from cryptographic attack comprising: means for deterministically introducing non-linearity into a PN signal to produce a deterministic bit pattern; and substituting means, coupled to the means for deterministically introducing non-linearity, for substituting the the deterministic bit pattern for the PN signal, whereby the PN signal is protected from cryptographic attack.
Claim 24
Independent Claim
83 words
An apparatus for protecting the pseudorandom (PN) sequence generated by a Linear Feedback Shift Register (LFSR) from cryptographic attack comprising: LFSR means for producing a PN sequence; altering means, coupled to the LFSR means, for altering at least one bit of the PN sequence to produce a deterministic bit pattern; and substituting means, coupled to the altering means, for substituting the deterministic bit pattern for the PN sequence, whereby non-linearity is deterministically introduced into the PN signal to protect it from cryptographic attack.
Claim 25
Independent Claim
83 words
An apparatus for protecting the pseudorandom (PN) sequence generated by a Linear Feedback Shift Register (LFSR) from cryptographic attack comprising: LFSR means for producing a PN sequence; altering means, coupled to the LFSR means, for altering at least one bit of the PN sequence to produce a deterministic bit pattern; and substituting means, coupled to the altering means, for substituting the deterministic bit pattern for the PN sequence, whereby non-linearity is deterministically introduced into the PN signal to protect it from cryptographic attack.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1994-10-21 | 1995-04-22 | 1995-10-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-10-21 | 1999-04-22 | 1999-10-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-10-21 | 2003-04-22 | 2003-10-22 | $7700.00 | Window Closed / Lapsed |