CA1162623A - Two level encripting of rf signals - Google Patents
Two level encripting of rf signalsInfo
- Publication number
- CA1162623A CA1162623A CA000380037A CA380037A CA1162623A CA 1162623 A CA1162623 A CA 1162623A CA 000380037 A CA000380037 A CA 000380037A CA 380037 A CA380037 A CA 380037A CA 1162623 A CA1162623 A CA 1162623A
- Authority
- CA
- Canada
- Prior art keywords
- key
- enciphering
- receiver
- enciphered
- deciphering
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0891—Revocation or update of secret information, e.g. encryption key update or rekeying
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L2209/00—Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
- H04L2209/60—Digital content management, e.g. content distribution
- H04L2209/601—Broadcast encryption
Landscapes
- Engineering & Computer Science (AREA)
- Computer Security & Cryptography (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)
- Storage Device Security (AREA)
- Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
- Circuits Of Receivers In General (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A system for enciphering information bearing RF signals in digital form utilizes a first key common to all receivers.
There are means to change the first key which means include, at the transmitter, means to send individual messages to each receiver, each message being itself enciphered in a second key which is peculiar to only one receiver or small group of receivers and which message includes a change of the first enciphering key. At each receiver there are means responsive to the correct address in a key change message which will thereafter permit the deciphering of the key change message in the key peculiar to a particular receiver or small group of receivers. The new first key is then used at the receiver to decipher subsequent information bearing messages.
A system for enciphering information bearing RF signals in digital form utilizes a first key common to all receivers.
There are means to change the first key which means include, at the transmitter, means to send individual messages to each receiver, each message being itself enciphered in a second key which is peculiar to only one receiver or small group of receivers and which message includes a change of the first enciphering key. At each receiver there are means responsive to the correct address in a key change message which will thereafter permit the deciphering of the key change message in the key peculiar to a particular receiver or small group of receivers. The new first key is then used at the receiver to decipher subsequent information bearing messages.
Description
~ i6~623 SUMMARY OF THE INVENTION
The present invention relates to means for enciphering or encripting messages in digital format and which may have par-ticular application to the communications industry. The invention will be described in connection with the enciphering and decipher-ing of audio signals, for example those usable in some form of subscription radio or cable format. The invention has substan-tially wider application and may be usable wi~h the enciphering of video signals, for example for a subscription television broad-cast or for cable television, and also has utility in the area of satellite transmissions, both of audio type signals, video signals and other forms of information, such as data which can be transmitted in digital form. The invention will be described in the context of a separate deciphering key for each receiver.
However, the principles disclosed are equally applicable with a separate deciphering key for each small group of receivers.
Use of the term receiver should be understood to include a small group of receivers. What is important is not to use a deciphering key comrnon to more than a small number of individual subscribers.
A primary purpose of the invention is an enciphering system of the type described which has two levels of security~
the first level providing enciphering of the information bearing signals, with the second level of security being used to encipher changes in the code or key for deciphering the information bear-ing messages at the first level of security.
Another purpose is an enciphering system of the type described in which the second level of security includes a sep-arate independent enciphering key for each receiver in the system.
Another purpose is an enciphering system of the type described including a transmitter which will regularly broadcast or transmit information bearing messages in enciphered form in - a particular key, which key may be changed on a periodic basis.
,.
The present invention relates to means for enciphering or encripting messages in digital format and which may have par-ticular application to the communications industry. The invention will be described in connection with the enciphering and decipher-ing of audio signals, for example those usable in some form of subscription radio or cable format. The invention has substan-tially wider application and may be usable wi~h the enciphering of video signals, for example for a subscription television broad-cast or for cable television, and also has utility in the area of satellite transmissions, both of audio type signals, video signals and other forms of information, such as data which can be transmitted in digital form. The invention will be described in the context of a separate deciphering key for each receiver.
However, the principles disclosed are equally applicable with a separate deciphering key for each small group of receivers.
Use of the term receiver should be understood to include a small group of receivers. What is important is not to use a deciphering key comrnon to more than a small number of individual subscribers.
A primary purpose of the invention is an enciphering system of the type described which has two levels of security~
the first level providing enciphering of the information bearing signals, with the second level of security being used to encipher changes in the code or key for deciphering the information bear-ing messages at the first level of security.
Another purpose is an enciphering system of the type described in which the second level of security includes a sep-arate independent enciphering key for each receiver in the system.
Another purpose is an enciphering system of the type described including a transmitter which will regularly broadcast or transmit information bearing messages in enciphered form in - a particular key, which key may be changed on a periodic basis.
,.
-2 -The change of key i5 itself enciphered in a second key, there being an individual second key for each independent receiver in the system.
Other purposes will appear in the ensuing specifica-tion, drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
.
The invention is illustrated diagrammatically in the following drawings wherein:
Figure 1 is a block diagram of a transmitter usable in a system of the type described, and Figure 2 is a block diagram of the receiver usable with the transmitter of Figure 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As indicated above, the two level security enciphering concept disclosed herein has application in a wide variety of communication systems. It is usable in satellite transmission, subscription television, subscription radio, cable systems and various forms of data transmission. The following description will be particularly applicable to the enciphering of digital audio information, although quite obviously, when considering the above comments, the invention should not be so limited.
In Figure 1 a source of audio information in digital form is indicated at 10 and is connected to a data enciphering circuit 12 which may, for example, utilize a Fairchild 9414 as .~ the basic integrated circuit for encipherng the digitized audio information~ The source of digital audio information is connected to the data port of enciphering circuit 12. A key generator ; 14 is connected to the key port of enciphering circuit 12 and will provide the key for use in enciphering the digitized audio information. Thus, the output from enciphering circuit 12 is the digitized audio information enciphered in a particular key referred to hereinafter as the first key.
., .
; .
l 162623 The output signal from circuit 12 will pass to a signal combiner 16 and then to a modulator 18 which will transmit the information in a form appropriate for the particular medium, whether it be broadcast, cable or satellite.
As indicated above, the first key will be changed on some type of regular basis to provide a more secure system.
An initiate key change circuit is indicated at 20 and will effect the formation of a new key by key generator 14. The new key will then be applied in block 12 for the enciphering of the dig-itized audio information. The initiate new key signal is alsoapplied to an address sequencer 22 which will effect a search of valid subscriber addresses stored in a random access memory or subscriber data base 24. The subscriber list may not be searched in any particular order, as what is important is to insure that each subscriber whose address is still valid will be addressed any time there is a key change.
Connected to the subscriber data base 24 is a key gen-erator 26 which may be in the form of a read only memory or ROM
and which will include a separate independent key for every subscriber in the overall system. The output from key generator 26 is connected to a key enciphering circuit 28 which will receive at its data port the new key from key generator 14. In this connection, key generator 14 may be a random number generator which creates independent non-repetitive keys. The new key provided at the data port will be enciphered by the series of keys provided from key generator 26 with the result that each message will include an address and an enciphered new key with the enciphering being done in a second key which is different for each receiver. This message is the output from circuit 28 and is connected to the signal combiner for subsequent transmission as described above. Thus, every time there is to be a change in the first key for enciphering the information bearing signals, this change in key itself is enciphered in a message which includes I i626Z3 an address and the first key enciphered in a second key with the second key being peculiar to only a single receiver.
Re~erring to the receiver shown in Figure 2, the inform-ation bearing and key change messa~es described in connection with Figure 1 are received at a demodulator 30 which provides the control and information bits to a demultiplexer 32. There are two outputs from demultiplexer 32. One output, designated the audio channel at 34, is connected to a data deciphering circuit 36 which has a data port and a key port. The enciphered information bearing signal will be provided at the data port and the output from data encipher circuit 36 will be the audio information in usable form.
A memory 38 which will contain the particular key or first key usable at a specific time is connected to the key port of data deciphering circuit 36 and thus will provide the means for deciphering the coded information bearing signals. Again, the particular integrated circuit for the data deciphering circuit may be a Fairchild 9414 suitably connected for deciphering.
The second output from the demultiplexer 32 is a control channel indicated at 40 which is connected to a first data selec-tor and buffer amplifier circuit 42 and a second similar circuit 44. Circuit 42 will select the address portion of a control message, whereas, circuit 44 will select the message portion.
Circuit 42 is connected to a comparator 46 wherein the address portion of the message is compared with a hard-wired address in a ROM 48. Assuming there is a valid comparison and thus that the message is for that particular receiver, there will be an output from comparator 46 to a gate 50 and to a random access memory (RAM) 52. RAM 52 will receive the enciphered key portion of the message from data selector 44 with this key being temporarily stored in the RAM. When an appropriate signal is received from comparator 46, the enciphered message in the RAM will be passed through gate 50 to the data port of a second data deciphering circuit 54. The key port of data deciphering circuit 5~ is connected to a ROM 56 which will have a hard-wired key peculiar to a particular receiver. Thus, the enciphered new key, or first key, will be received at the data port of circuit 54 and the key for deciphering such message will be received at the key port from ROM 56. Again, circuit 54 may utilize the above-described integrated circuit or one of like kind and quality. The output from circuit 54 will be the deciphered new first key which is stored in memory 38 so that subsequent data bearing messages may be deciphered.
To summarize, the two level security system disclosed herein utilizes a first key to encipher information bearing mes-sages in digital form. The first key will be changed on either a regular or random basis, depending upon the security safeguards necessary in the particular communications environment. When there is to be a change in the first key, the new first key is itself enciphered in a message which is peculiar to each individual receiver or to a small group of subscriber receivers as described above. Such message will include the address of a receiver and the first key enciphered in a code peculiar to that particular receiver. Thus, there will be a series of such messages, one for each receiver in the system. At the receiver the enciphered first key will be deciphered by the second key peculiar to that receiver. The deciphered first key will then be utilized in deciphering subsequent information bearing digital messages.
Whereas the preferred form of the invention has been shown and described herein, it should be realized that there may be many modiEications, substitutions and alterations thereto.
., .
,.
..
Other purposes will appear in the ensuing specifica-tion, drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
.
The invention is illustrated diagrammatically in the following drawings wherein:
Figure 1 is a block diagram of a transmitter usable in a system of the type described, and Figure 2 is a block diagram of the receiver usable with the transmitter of Figure 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As indicated above, the two level security enciphering concept disclosed herein has application in a wide variety of communication systems. It is usable in satellite transmission, subscription television, subscription radio, cable systems and various forms of data transmission. The following description will be particularly applicable to the enciphering of digital audio information, although quite obviously, when considering the above comments, the invention should not be so limited.
In Figure 1 a source of audio information in digital form is indicated at 10 and is connected to a data enciphering circuit 12 which may, for example, utilize a Fairchild 9414 as .~ the basic integrated circuit for encipherng the digitized audio information~ The source of digital audio information is connected to the data port of enciphering circuit 12. A key generator ; 14 is connected to the key port of enciphering circuit 12 and will provide the key for use in enciphering the digitized audio information. Thus, the output from enciphering circuit 12 is the digitized audio information enciphered in a particular key referred to hereinafter as the first key.
., .
; .
l 162623 The output signal from circuit 12 will pass to a signal combiner 16 and then to a modulator 18 which will transmit the information in a form appropriate for the particular medium, whether it be broadcast, cable or satellite.
As indicated above, the first key will be changed on some type of regular basis to provide a more secure system.
An initiate key change circuit is indicated at 20 and will effect the formation of a new key by key generator 14. The new key will then be applied in block 12 for the enciphering of the dig-itized audio information. The initiate new key signal is alsoapplied to an address sequencer 22 which will effect a search of valid subscriber addresses stored in a random access memory or subscriber data base 24. The subscriber list may not be searched in any particular order, as what is important is to insure that each subscriber whose address is still valid will be addressed any time there is a key change.
Connected to the subscriber data base 24 is a key gen-erator 26 which may be in the form of a read only memory or ROM
and which will include a separate independent key for every subscriber in the overall system. The output from key generator 26 is connected to a key enciphering circuit 28 which will receive at its data port the new key from key generator 14. In this connection, key generator 14 may be a random number generator which creates independent non-repetitive keys. The new key provided at the data port will be enciphered by the series of keys provided from key generator 26 with the result that each message will include an address and an enciphered new key with the enciphering being done in a second key which is different for each receiver. This message is the output from circuit 28 and is connected to the signal combiner for subsequent transmission as described above. Thus, every time there is to be a change in the first key for enciphering the information bearing signals, this change in key itself is enciphered in a message which includes I i626Z3 an address and the first key enciphered in a second key with the second key being peculiar to only a single receiver.
Re~erring to the receiver shown in Figure 2, the inform-ation bearing and key change messa~es described in connection with Figure 1 are received at a demodulator 30 which provides the control and information bits to a demultiplexer 32. There are two outputs from demultiplexer 32. One output, designated the audio channel at 34, is connected to a data deciphering circuit 36 which has a data port and a key port. The enciphered information bearing signal will be provided at the data port and the output from data encipher circuit 36 will be the audio information in usable form.
A memory 38 which will contain the particular key or first key usable at a specific time is connected to the key port of data deciphering circuit 36 and thus will provide the means for deciphering the coded information bearing signals. Again, the particular integrated circuit for the data deciphering circuit may be a Fairchild 9414 suitably connected for deciphering.
The second output from the demultiplexer 32 is a control channel indicated at 40 which is connected to a first data selec-tor and buffer amplifier circuit 42 and a second similar circuit 44. Circuit 42 will select the address portion of a control message, whereas, circuit 44 will select the message portion.
Circuit 42 is connected to a comparator 46 wherein the address portion of the message is compared with a hard-wired address in a ROM 48. Assuming there is a valid comparison and thus that the message is for that particular receiver, there will be an output from comparator 46 to a gate 50 and to a random access memory (RAM) 52. RAM 52 will receive the enciphered key portion of the message from data selector 44 with this key being temporarily stored in the RAM. When an appropriate signal is received from comparator 46, the enciphered message in the RAM will be passed through gate 50 to the data port of a second data deciphering circuit 54. The key port of data deciphering circuit 5~ is connected to a ROM 56 which will have a hard-wired key peculiar to a particular receiver. Thus, the enciphered new key, or first key, will be received at the data port of circuit 54 and the key for deciphering such message will be received at the key port from ROM 56. Again, circuit 54 may utilize the above-described integrated circuit or one of like kind and quality. The output from circuit 54 will be the deciphered new first key which is stored in memory 38 so that subsequent data bearing messages may be deciphered.
To summarize, the two level security system disclosed herein utilizes a first key to encipher information bearing mes-sages in digital form. The first key will be changed on either a regular or random basis, depending upon the security safeguards necessary in the particular communications environment. When there is to be a change in the first key, the new first key is itself enciphered in a message which is peculiar to each individual receiver or to a small group of subscriber receivers as described above. Such message will include the address of a receiver and the first key enciphered in a code peculiar to that particular receiver. Thus, there will be a series of such messages, one for each receiver in the system. At the receiver the enciphered first key will be deciphered by the second key peculiar to that receiver. The deciphered first key will then be utilized in deciphering subsequent information bearing digital messages.
Whereas the preferred form of the invention has been shown and described herein, it should be realized that there may be many modiEications, substitutions and alterations thereto.
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..
Claims (4)
1. In a system for enciphering digital information bearing signals, means for using a first key to encipher the digital signals, means for simultaneously transmitting the first key enciphered digital signals to a plurality of re-ceivers, means for changing said first enciphering key applied to said digital signals, means for enciphering, in a second enciphering key, an information message as to the change in said first enciphering key, said second enciphering key being different for each of said plurality of receivers, and means for transmitting said enciphered information message, separately to each of said plurality of receivers, each such enciphered information message being enciphered in a different second key.
2. The system of claim 1 further characterized in that said information message includes an address for each of said plurality of receivers.
3. In a receiver for deciphering enciphered digital information bearing signals, first deciphering means responsive to a system common first deciphering key for deciphering said digital signals, means for changing said system common first key including second deciphering means responsive to a message enciphered in a second key and which includes a change in said first key, said second deciphering means being responsive to a key peculiar to only one receiver.
4. The receiver of claim 3 further characterized by and including address means responsive to an address portion of said key change message for enabling said second decipher-ing means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16098580A | 1980-06-19 | 1980-06-19 | |
| US160,985 | 1980-06-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1162623A true CA1162623A (en) | 1984-02-21 |
Family
ID=22579317
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000380037A Expired CA1162623A (en) | 1980-06-19 | 1981-06-17 | Two level encripting of rf signals |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS5730438A (en) |
| AU (1) | AU539774B2 (en) |
| BR (1) | BR8103848A (en) |
| CA (1) | CA1162623A (en) |
| DE (1) | DE3124150C2 (en) |
| FR (1) | FR2485305A1 (en) |
| GB (1) | GB2079109B (en) |
| GR (1) | GR74584B (en) |
| IL (1) | IL63102A (en) |
| MX (1) | MX150514A (en) |
| NL (1) | NL8102940A (en) |
Families Citing this family (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1177558A (en) * | 1982-04-15 | 1984-11-06 | Groupe Videotron Ltee. (Le) | Cable network data transmission system |
| US4531020A (en) * | 1982-07-23 | 1985-07-23 | Oak Industries Inc. | Multi-layer encryption system for the broadcast of encrypted information |
| JPH0614641B2 (en) * | 1983-03-29 | 1994-02-23 | 富士通株式会社 | Key information delivery processing method |
| JPS6032449A (en) * | 1983-08-01 | 1985-02-19 | Matsushita Electric Ind Co Ltd | Ciphered digital broadcast equipment |
| EP0167442A3 (en) * | 1984-06-29 | 1986-12-30 | Fairchild Weston Systems Inc. | Secure communication system |
| US4751732A (en) * | 1984-07-06 | 1988-06-14 | Kabushiki Kaisha Toshiba | Broadcasting system |
| JPS6120442A (en) * | 1984-07-09 | 1986-01-29 | Toshiba Corp | Chargeable broadcasting system |
| DE3439120A1 (en) * | 1984-10-25 | 1986-05-07 | Philips Kommunikations Industrie AG, 8500 Nürnberg | Method for identifying a subscriber station of a telecommunications network |
| DE3501178A1 (en) * | 1985-01-16 | 1986-07-17 | Blaupunkt-Werke Gmbh, 3200 Hildesheim | METHOD AND CIRCUIT ARRANGEMENT FOR PREVENTING THE UNAUTHORIZED RECEPTION OF ENCRYPTED TELEVISION SIGNALS |
| JPH0685517B2 (en) * | 1985-06-28 | 1994-10-26 | ソニー株式会社 | Information service system |
| US4866770A (en) * | 1986-07-08 | 1989-09-12 | Scientific Atlanta, Inc. | Method and apparatus for communication of video, audio, teletext, and data to groups of decoders in a communication system |
| DE3715081A1 (en) * | 1987-05-06 | 1988-11-17 | Siemens Ag | Method for encrypting digital video signals |
| DE3731532A1 (en) * | 1987-09-18 | 1989-03-30 | Siemens Ag | Process for transmitting encoded picture signals |
| DE3822354A1 (en) * | 1988-07-01 | 1990-01-04 | Siemens Ag | Method and arrangement for scrambling image signals |
| DE4419634A1 (en) * | 1994-06-04 | 1995-12-07 | Esd Vermoegensverwaltungsgesel | Decryption device for digital information and method for performing the encryption and decryption of this |
| DE4420970A1 (en) * | 1994-06-16 | 1995-12-21 | Esd Vermoegensverwaltungsgesel | Decryption device for decryption algorithms and method for performing the encryption and decryption thereof |
| DE4420967C2 (en) * | 1994-06-16 | 2000-02-10 | Esd Vermoegensverwaltungsgesel | Decryption device for digital information and method for carrying out the encryption and decryption of this using the decryption device |
| DE19619299A1 (en) * | 1996-05-13 | 1997-12-18 | Siemens Ag | Code key distribution method in fibre distributed data interface (FDDI) transmission network |
| DE19649292A1 (en) * | 1996-11-28 | 1998-06-04 | Deutsche Telekom Ag | Access protection method for pay television |
| GB2393367B (en) * | 1999-04-16 | 2004-05-26 | Fujitsu Ltd | Optical line terminal |
| JP4201430B2 (en) | 1999-04-16 | 2008-12-24 | 富士通株式会社 | Optical subscriber line termination equipment |
| GB2355819A (en) * | 1999-10-26 | 2001-05-02 | Marconi Comm Ltd | Authentication of data and software |
| GB2367726B (en) * | 2000-10-07 | 2003-04-23 | Complementary Tech Ltd | Communications with remote embedded applications |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH516854A (en) * | 1969-11-29 | 1971-12-15 | Ciba Geigy Ag | Method and device for encrypted transmission of information |
| DE2706421C2 (en) * | 1977-02-16 | 1979-03-15 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Procedure for setting ciphertext generators in encryption devices |
| CH604432A5 (en) * | 1977-03-16 | 1978-09-15 | Europ Handelsges Anst |
-
1981
- 1981-06-15 IL IL63102A patent/IL63102A/en unknown
- 1981-06-16 AU AU71871/81A patent/AU539774B2/en not_active Ceased
- 1981-06-17 BR BR8103848A patent/BR8103848A/en unknown
- 1981-06-17 CA CA000380037A patent/CA1162623A/en not_active Expired
- 1981-06-18 GR GR65275A patent/GR74584B/el unknown
- 1981-06-18 NL NL8102940A patent/NL8102940A/en not_active Application Discontinuation
- 1981-06-18 FR FR8112026A patent/FR2485305A1/en active Pending
- 1981-06-19 GB GB8119018A patent/GB2079109B/en not_active Expired
- 1981-06-19 JP JP9515581A patent/JPS5730438A/en active Granted
- 1981-06-19 DE DE3124150A patent/DE3124150C2/en not_active Expired
- 1981-06-19 MX MX187888A patent/MX150514A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| NL8102940A (en) | 1982-01-18 |
| AU539774B2 (en) | 1984-10-18 |
| IL63102A (en) | 1984-03-30 |
| GB2079109B (en) | 1984-04-11 |
| BR8103848A (en) | 1982-03-09 |
| JPS5730438A (en) | 1982-02-18 |
| GB2079109A (en) | 1982-01-13 |
| IL63102A0 (en) | 1981-09-13 |
| JPS63976B2 (en) | 1988-01-09 |
| DE3124150C2 (en) | 1985-03-28 |
| GR74584B (en) | 1984-06-29 |
| DE3124150A1 (en) | 1982-03-18 |
| FR2485305A1 (en) | 1981-12-24 |
| MX150514A (en) | 1984-05-16 |
| AU7187181A (en) | 1981-12-24 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |