FR2812147A1 - Method of security processing of data flow such as e.g. MP3 data stream by transmitting processes data stream back to external device that recombines of processes part with major fraction to produce flux of output information - Google Patents

Abstract

A small fraction of a transmission (120) is sent to a microchip, which decodes and watermarks (130,135) the small fraction. The processed part is transmitted (140) to an external device that recombines (150) of the processes part (A') with the major fraction (B) in order to produce a flux of an output information (A'+B) for MP3 decoding (160).

Description

The invention relates to a method for processing a digital information flow.

  safety circuits.

  It particularly concerns the processing of representative information.

  of reproducible sequences such as audio, video, tex-

  tuelles or the like. The invention will be described mainly in the context of audio sequences.

  because this is the most immediate application given the capabilities

  current broadcast network tees; however, the invention may be

  transposed directly to the acquisition of other types of sequences, no-

  as much video data (still images or moving pictures from television

  sion) or textual sequences. It applies in the same way to the ac-

  sequence of sequences forming computerized data files

  that, for example data necessary for downloading a software

  sky, or to allow the execution by the user of software requiring an exchange of data with a remote site; this app lends itself

  especially in the area of downloaded electronic games.

  It often happens that one wishes to carry out one or more milking

  information on such a flow of information, processing (s) carried out in a micro-

  security circuit, for example the microcircuit of a smart card, capable of storing information in a permanent memory and of performing cryptographic calculations on information (keys) stored in

  this microcircuit, and not legible from the outside of the microcircuit.

  The processing to be carried out is in particular: - the decryption and / or the re-encryption of the stream; - control or generation of a certificate or electronic signature of the flow;

  - "watermarking", namely the encoding or decoding of auxiliary information

  filial watermark (i.e. superimposing information on the flow

  imperceptible to human senses, but which can be detected by appropriate means); such systems are for example described in USA-5,687,191 (Solana Technology Development Corp.);

  - extracting or adding information to the stream by demultiplexing or multi-

plex;

  - all operations usually carried out in a dry microcircuit

  curity, in particular controls of all kinds, accounting, pay-

storage.

  The advantage of carrying out these operations in a security microcircuit is generally to hide part of the information used in the processing,

  and / or to guarantee that such or such treatment is carried out according to

  imposed. Thus, in an example of application which will be explained in more detail below, it is desired that a stream of music, digitized and compressed according to

  ISO / IEC 11172-3, either encrypted, transmitted identically to several recipients

  res, deciphered and tattooed with identification information from the micro-

  circuit entrusted to each user. The advantage of performing the decryption and watermarking operations in a security microcircuit, rather than in a microcomputer for example, is that it is thus ensured that the flow of decrypted and uns watermarked information is not not accessible any more

  of course that the decryption key, nor that used to encode the tattoo-

  ge. The need for such processing is apparent in particular from WO-A-00/11866 for "Secure device for decoding encrypted and compressed information"

  (Innovatron SA), which describes a particularly advanced implementation

  signal decryption and decompression tagger using

a microcircuit card.

  We can also consider the problem of extracting from an audio or video stream information relating to the management of exploitation rights, such as identification of the authorized receiving device, number of copies

  authorized, prices, and to carry out operations such as identity control

  tification and / or copy rights, decrementation of the number of copies

  authorized, payment, watermarking of the number of copies remaining and / or the

  dentifier of the authorized receiving device for the resulting information. The need for such treatments is apparent in US-A-5,892,900 (Intertrust

Technologies Corp.).

  An implementation according to current techniques would consist in transferring

  The microcircuit information, carry out the treatments there and restore the information

  mation treated. It faces two practical limitations:

  - the transmission speed of existing microcircuit readers: those

  these usually communicate with a bit rate of 9.6 kbit / s, and the useful bit rate is even lower, of the order of 5 kbit / s, whereas, in an example of music compressed at 128 kbit / s, it would be necessary a much higher bit rate of 256 kbit / s (factor 2 from the double incoming stream

  and outgoing), to process information at the speed of listening.

  - the processing capacity (decryption and watermarking) of the microcircuit

is limited.

  One of the aims of the invention is to overcome this difficulty of practical implementation, by a means making it possible to reduce the amount of information

  exchanged with the microcircuit without compromising the character-

  safety of the treatments carried out in the microcircuit - in particular -

  without increasing the risk of fraud.

  Essentially, the invention proposes to select a small fraction of the information (typically less than 20% and for example between 5% and 1%, even less than 1%) which will be extracted from the total flow for transmission and processing by the microcircuit , then recombine it with the untreated part of the flow. The fraction of the flow extracted for processing in the card

  will be chosen so that its presence is significant, even essential

  tielle, for the proper performance of the desired operating functions of

  all of the information. For example, in the case of a music stream

  than digitized, in the absence of a correct security treatment by the

  te, passages of music would periodically be missed, or

  periodically distorted, making the reproduction of music

unacceptable.

  In this way, it is possible to perform relatively complex processing (decryption, watermarking, key calculation, etc.) with microcircuit cards and traditional readers, the processing capacity of which would be largely insufficient to allow processing of the data. 'together

  of the flow, which makes it possible to implement these treatments which

would otherwise be excluded.

  More specifically, the invention relates to a method for processing an information flow

  training by a security microcircuit, in particular a chip card microcircuit, this microcircuit cooperating with an external device capable of producing the flow of information in the form of digital data and

  use this information flow after processing by the microcircuit, character-

  laughed at by the following steps: a) by the external device, production of the information flow, b) by the external device, separation of the incident information flow into

  two separate fractions, with a minor fraction and a ma-

  jeure, the major fraction having a size and / or a flow of information

  significantly higher than the minor fraction,

  c) transmission of the minor fraction from the external device to the microcir-

  cooked, d) within the microcircuit, safe treatment of the minor fraction, e) transmission of the treated minor fraction from the microcircuit to the external device, f) by the external device, recombination of the minor fraction treated with the major fraction so as to produce an outgoing information flow,

  g) by the external device, use of the outgoing information flow.

  According to various advantageous subsidiary implementations:

  - the safety treatment in step d) is a treatment for the group

  taking: decryption or encryption of the stream; control or generation

  a certificate or electronic signature of the flow; encoding or decoding

  age of auxiliary information tattooed in the flow; extracting or adding information to the stream by demultiplexing or multiplexing; flow validity check; management of rights to use flow information; combination of two or more of the above treatments;

  - the external device comprises a source device and a device used

  separate sator, the microcircuit cooperating with the user device, steps a) and b) are implemented in the source device, and step f) is implemented in the user device; - after step b) of separation and before step c) of transmission, it is

  provided for a processing step, in particular encryption, for the frac-

  minor action (A) by the external device, step d) of secure processing

  ritaire implemented within the microcircuit being a step of a symmetrical processing, in particular a step of deciphering; - the security processing in step d) includes a key transcoding,

  comprising a decryption with a first key then a re-encryption

ment with a second key;

  the separation of step b) comprises a temporal separation, operated

  rée by cutting the incident flow into time intervals, and / or a separation according to the informational content of the component data

  the incident flow, operated by extraction of data fields from

  predetermined ture; - separation of step b) and / or security treatment is a function

  of parameters influencing the perceptibility of separation and / or treatment

  and selected to reduce their perceptibility;

  - the safety treatment in step d) also includes the production

  tion of a key able to allow the decryption of the major fraction by the external device;

  - the size and / or the information rate of the minor fraction is less

  less than 20% of the total flow, preferably between 5% and 1% of the

  total flow, advantageously less than 1% of the total flow.

  We will now describe an example of implementation of the invention, in

reference to the accompanying drawings.

  Figure 1 schematically illustrates the different stages of the process.

die of the invention.

  FIG. 2 illustrates, in the form of functional blocks, different elements

  involved in a particular implementation of the method of the invention.

  The implementation of the invention involves, as illustrated in FIG. 1, at least two separate organs, namely a safety microcircuit 100 and,

  on the other hand, a set which will be called "external device" 200, cor-

  responding to the external environment, not secure or partially dry

curized, of this microcircuit 100.

  The safety microcircuit can for example be an ST16SF48 from STMi-

  croelectronics, embedded in a card according to ISO / IEC 7816-1 to -3 and connected to its environment by a microcircuit card reader conforming to

  these standards or equivalent (both removable and per-

  manente), for example through a USB type bus.

  In the example which will be described, the external device 200 consists of a "user device" 210 and a "source device" 220 connected together by a communication channel such as an Internet link or any

another teletransmission channel.

  This implementation in which the external device 200 consists

  of two separate and distant organs 210 and 220 is however not li-

  mitative, and the invention applies equally to the processing of information

  produced and used by a single device.

  In the example which will be described, the user device 210 can in particular

  ment be a device type "Internet tuner" as described in WO-

  A-00/11867 for "Method of certified delivery of an audio, video or text sequence" (Innovatron SA) and WO-A-00/11868 for "Method of

  delivery and payment of an audio, video or text sequence "(In-

  novatron SA). These requests describe means making it possible to acquire, for listening, audio sequences, typically musical works.

  such as music or individual tracks from one

  registration, suitably selected by the user. The pieces

  are downloaded as digital data packets

  ques possibly signed, encrypted and compressed, and transmitted from

  a central site (source device) to the user device.

  The user device 210 for this purpose comprises means, integrated or

  separate, sound reproduction, various decompression circuits,

  encryption, payment, access control, etc., in particular circuits implementing one or more microcircuit cards, as well as means of connection to a remote site (central site or else relocated to several sites). The download is typically carried out via the Internet, i.e.

  by interconnected global networks connecting sites and users

  variable and multiple routes for data transmission

born in digital form.

  The source device 220 is for example a configured microcomputer

  as an Internet server, or even a simple storage medium such as this

derom or DVD-ROM.

  The original information intended to be processed is first digitized and advantageously compressed and coded, for example, in the case of

  music, by ISO / IEC 11172-3 layer 3 ('MP3') coding (step 105).

  Characteristically of the invention, the resulting flow 110 is then separated into two distinct fractions, a minor fraction A (representing for example between 5% and 1% by volume of the overall flow), and a major fraction B (therefore representing respectively between 95% and 99% of the overall flow A + B). Flow A is defined to contain information

  necessary, even essential, for a correct exploitation of the global flow

  ball A + B. The separation of step 110 can be carried out in different ways,

  which can also be combined with one another.

  In a first variant, the separation is a temporal separation.

  The information is then divided into time intervals corresponding to the

  transmission time or, for an audio or video stream, the remaining time

  titution to human senses. A predetermined fraction of these intervals constitutes A, and the rest B. This temporal selection finds its justification in the fact that an audio or video message periodically amputated from a significant part of its content becomes unusable. For example, the

  flux A retains 0.2 second intervals every 4 seconds.

  As the flow of audio or video information is frequently, by its co-

  even, structured in frames representing distinct time intervals (called "frames" in ISO / IEC 11172-3), this time division then amounts to retaining for the flow A a fraction of the frames: for example, if a frame lasts 0.025 s, then flow A will retain 8 frames on

  160. This is an example of a case where it may be advantageous for the frac-

  minor proportion represents between 5% and 1% of the total A + B flow, this fraction being large enough to ensure an unacceptable degradation of the content if it is not reproduced, while greatly reducing the

charge of the microcircuit.

  In a second variant, the separation is a separation by nature of information.

  The information flow is divided by a factor of 200, which allows

  reduce the load on the microcircuit to less than 1% of the total flow A + B while guaranteeing security, preferably selecting for flow A the information of predetermined nature which is most important for the intelligibility of the flow by human senses and / or those adapted to

  processing considered and / or those necessary for the operation of the

  seems to be information and / or whose reconstruction in the event of alteration is the most difficult. For example, according to ISO / IEC 11172-3 each frame is divided into numerous fields, and to make it completely unusable

  an ISO / IEC 11172-3 layer III audio stream just encrypt the Huf- field

  fmancodebits (see 2.4.1.7 of the standard, page 19), or even the signx and signy bits alone, or a predetermined number of signx and signy bits chosen to be those of certain values of the index /, for example as a predetermined number of those for which Ixl and

  IYI are the largest, possibly restricting themselves to an inter-

valley of /.

  In the case of a treatment consisting of a tattoo, we will retain in

  flow A the information coding the quantities which, taking into account the system

  teme, are to be modified for the inscription of the watermark it will be for example information in a predetermined frequency band and / or that whose amplitude is the largest and / or the most constant and / or in the

  limit of a limit of quantity or flow of predetermined information li-

  reducing the amount of information included in flow A.

  In addition, the two variants just described can be combined

  born between them, in various ways. So:

  - we can simply retain only a fraction of the information ("se-

  lection by nature "above) of a temporal fraction (" temporal selection "above) of the flux, which multiplies the reduction effects of flux A. - we can also make a temporal selection according to the adequacy to the treatment to perform: we examine the time intervals of the flow

  to determine their suitability for the treatment to be performed (such as ta-

  tapping) and preferentially select those of the intervals of the stream which are most apt to undergo the treatment (with a minimum degradation of the perceived quality and / or a better coding capacity, these parameters varying considerably according to the time intervals) , within the limit of a predetermined ceiling limiting the amount of information included in flow A. The combination of the two selection techniques can make it possible to have for A a fraction even lower than 1% of the total information, this

  which allows the use of microcircuits and microcircuit readers ac-

  tually available, without waiting for future performance improvements

  mances, while maintaining the level of security required for processing

(deciphering and tattooing).

  Before transmission to the user device, it is often useful to provide, at the server level, an additional step 115 for processing the stream A, for example an encryption step using a secret key K and a symmetric algorithm. .

  The flows A and B thus prepared by the source server 220 are then trans-

  set to the user device 210, which therefore receives these two streams A and B concurrently, for example multiplexed to allow their transmission over

a common channel.

  On reception, flow A is isolated and transmitted (at 120) to the sewer microcircuit.

  curity 100. This then decrypts the flow A (step 130) by means of the key K which it contains or which it is capable of recalculating. If you also want to tattoo the music before playing it, the microcircuit then operates a

  tattoo (step 135) by watermark inscription in stream A of an identi-

  reliable specific to the microcircuit (or another identifier specific to the card and / or the user)

  The resulting stream A 'is transmitted back (at 140) to the user device.

  The latter combines the streams A 'and B (step 150) and transforms the whole into a reproducible sound signal, for example by ISO / IEC decoding

  11172-3 layer 3 ('MP3') from step 160.

  The process just described can be the subject of different

adaptations or improvements.

  So, in the case of a temporal selection, it can be useful at a stage

  additional (located after encryption 115) to reorder the seg-

  in order to allow the easiest possible playback, without waiting at the start and with a minimum of memory in the playback device. Take the example of frames numbered consecutively from 01 to 30, multiple frames of 10 being part of flow A. It will be useful in this additional step to reorder the flow in order:

  10 01 02 03 04 05 06 07 08 09 20 11 12 13 14 15 16 17 18 19 30 21 22

23 24 25 26 27 28 29.

  In this way, the sound reproduction of the frames n 01 to 09 can be done while the frame n 10 is transmitted and processed by the microcircuit

  (steps 120 to 140), relatively long operations.

  Similarly frames # 20 and 30 will be processed during the restitution of the

frames 11 to 19 and 20 to 29.

  Another improvement consists in combining the technique of the invention

  with a different technique, in itself known and used in particular-

  Pay TV, which aims to reduce the quantification by another means

  t of information manipulated by the microcircuit (but in the only case

  conditional decryption processing).

  In this known technique: - a key K is chosen (possibly variable over time); - the audio or video stream F is encrypted with this key K, producing F '; - the key K is encrypted with another key, producing K '- the flow F' and the key K 'are combined by multiplexing; - the whole is transmitted to a decoder; - the decoder separates F 'and the key K'; - the decoder transmits the key K 'to the microcircuit; - the microcircuit decrypts the key K ', producing K; - the microcircuit transmits the key K to the decoder;

  - the decoder decrypts the stream F ', producing the original stream F.

  It will be noted that in this known technique the useful information F (audio or video) does not pass through the microcircuit, whereas it will do so in part

  in the system which is the subject of the present invention (with the characteristic advantage

  ristic to allow even an arbitrary processing in the microcircuit,

  such as a tattoo, useful information).

  Thus, the information restored in this known technique is identical to the original information, while the invention allows its partial processing in the microcircuit. In practice, the combination of information from the microcircuit and the main stream is done by decryption in the pay-TV technique, while it is done by addition or multiplexing.

in one form of the invention.

  This known technique can usefully be combined with that of the pre-

  invention, in particular to decipher the flow B. We can for example-

  ple add the following steps to the previous system: - to the source server, upstream of the encryption step 115: - we choose a random key KB, - we encrypt stream B with KB, and - we multiplex the value of KB with AT; - in step 115, KB and A are encrypted together with K (a separate step could be provided); - KB 'and A encrypted are transmitted to the user device (a separate step could be provided); - in step 120, KB 'and A encrypted are transmitted together to the security microcircuit (a separate step could be provided);

  - in step 130, KB and A are deciphered (a step could be provided

  adorned); - in step 140, KB and A ′ are transmitted to the user device (a separate step could be provided); - upstream of the recombination step 150: - the key KB of the stream A ′ is extracted, symmetrically to that of the multiplexing by the source server; and - we decipher the flow B with KB, symmetrically to that of

encryption by the source server.

  Note that, if we combine the encryption of stream B and the technique

  than reordering the frames exposed above, the KB key encrypts

  frant the frames n 11 to 19 must be in block n 10, and not in the

block 20.

  It may be useful to provide for the microcircuit to decipher the key K ', giving

  K, and re-encrypts it in a different way, giving K ".

  In addition, in addition to the encryption keys, information linked to the flow (such as reproduction rights) can be extracted from the

  flow and processed by the microcircuit.

  Thus, the processing 30 can include: decryption with a first key, and

  - re-encryption with a second key.

  This key transcoding authorizes for example the decryption in the user device of a stream coming from the server, in particular after

  payment, the re-encryption limiting its subsequent re-use to another app

  similarly designated by the reload key (for example

a particular player).

  FIG. 2 illustrates, in the form of functional blocks, different elements involved in a particular implementation of the process that we have just

to describe.

  This configuration is intended to allow the distribution of multi-content

  timedia (audio, video, games, etc.) from the source device (server) 220, where this multimedia content is prepared and made available as described, to the destination device 210 of a client : - by ensuring that the content will only be available to customers who have paid a viewing right, - by also making it possible to guarantee payments and enforce the rules defined by the rights holders (for example a limited number of authorized views),

  - finally providing a certain traceability allowing, in case of fraud

  to be able to go back to the server and / or determine the buyer at the

copy copy.

  The client's receiving device 210 is a hardware and software assembly constituted around a known type of equipment such as a microcomputer, digital TV decoder (in particular of the "set top box" type), or else

  mobile phone capable of exchanging consistent digital data

  GSM, WAP, GPRS, UMTS or other standards.

  Associated with this equipment: - client application software 211, the microcircuit 100, - possibly a mass storage means 213 such as hard disk, flash memory, etc., - a peripheral 214 for rendering multimedia content, by example

  television monitor, audio amplifier, personal digital assistant

* staff, CD burner, etc. Multimedia content is first prepared at the server level

source 220 as follows.

  This content, designated "valuable content" in FIG. 2, is accompanied by "usage rules" which define the restrictions on use, the number of copies used, the expiration period, etc. These rules may possibly be non-specific rules, applied by default when the content of value is not associated with any specific rule.

  Multimedia content can also include information,

  signed "worthless content", not requiring protective measures

  particular tion, for example biography of the performer, lyrics of a song, presentation jacket, etc. Usage rules are incorporated into valuable content, for example and

  in itself known by tattooing, then the whole is de-

  cut into blocks, signed and encrypted, to finally produce: - on the one hand the valuable content, in the form of signed and encrypted blocks, this valuable content incorporating the rules of use,

  - on the other hand, an associated "access ticket", which will allow control of access

  access to multimedia content and its return by the receiving device

  in the manner indicated below (the term "title" being understood

  of in its legal meaning (as in "transport ticket" or

  "debt obligation"), that is to say as a certificate evidencing a deed

  ridiculous or material capable of producing effects - here the authorization

  content reproduction or duplication), - and possibly worthless content, simply cut into

blocks.

  This data set is stored by the server 220.

  The server-client transaction is carried out securely between the service

  veur and the microcircuit 100 according to techniques known per se, the client application software 211 serving as a gateway between the server and

the microcircuit.

  To ensure security, the microcircuit and the server exchange certificates, with for example: - a first certificate, from the microcircuit to the server, to certify that the user of the microcircuit has paid the price corresponding to the content of precisely identified value, and - a second certificate, from the server to the microcircuit, for transmitting to the latter the access ticket, this ticket possibly containing a

decryption key.

  These certificates are signed and encrypted using keys kept from a

  securely in the microcircuit and in the server. The transactions

  tions between these two bodies are thus secured, even through a

  unsafe channel (telephone network, cable network, Internet, etc.).

  Once these operations have been carried out, all of the content blocks of-

  mandated (valuable content and worthless content) is transmitted to the device

reil recipient.

  Any operation from or to a device, including

  taken the local rendering device 214, can only be done through

  microcircuit 100, the latter responding only for this purpose to

  mandates duly signed and authenticated.

  After preparation and transfer of multimedia content, the destination device

  re has valuable content, encrypted with the rules that must re

  gir access, and possibly a set of non-secret information

  (worthless content, which can be displayed by the playback device

  tion 214, or simply ignored).

  We will first describe an implementation in which the valuable content is restored in "streaming" that is to say restored in a form

  intelligible to human senses as it is received, sensi-

  at the speed at which it is transmitted, without permanent storage

  in the user device (which stores only a limited amount of information

  mations, for example corresponding to one second of restitution for

  absorb short-term fluctuations in the means of transmission).

  The blocks are transmitted to the destination device which sends a decryption command to the microcircuit by passing the block to it. The microcircuit

  Of course, accepts these orders only if they have been suitable-

  signed and authenticated. It calculates the signature of the block and checks the access conditions, in particular the fact that the user has the right to receive the content in "streaming" and that he has paid the payment of the reading rights; for this he uses the access ticket he received following payment, with the rules which have been tattooed and / or included in the

valuable content.

  In accordance with the present invention, the content of value incorporating the rules is divided (step 110 of FIG. 1) into two distinct flows A and B in a relevant manner, that is to say so as to make the flow unusable.

  B alone, or flow A + B, without A having been further processed by the mid-

crocircuit.

  Flow B (major fraction, typically 95 or 99% by volume of total flow A + B) is encrypted with a first key, or possibly left in the clear. On the other hand, flow A, which must be treated with maximum security,

  is encrypted (step 115 in Figure 1), as are the rules and the first

  key mentioned above, so that it can only be deciphered later by

the safety microcircuit.

  Characteristically of the invention, only the stream A is transmitted to the mid

  crocircuit, or it will be deciphered and tattooed (steps 130 and 135 of figure 1).

  Optionally, the microcircuit can also re-encrypt flow A with

  a key associated with the particular restitution device 214.

  Furthermore, the microcircuit restores and transmits to the user device the first aforementioned key, that is to say the one which allows the decryption of the stream.

  B in case this has not been transmitted in clear.

  This decryption of stream B is operated outside the microcircuit, the memory and processing capacities of which would be insufficient to ensure

this operation in real time.

  The peripheral 214 can then reproduce the multimedia content.

  When "streaming" is not possible or not desired, the content is simply downloaded, that is to say that the corresponding information is stored in full and permanently in the means of

  storage 213 for later return.

  The procedure described above is then adapted as follows.

  The client application software 211 serves as a gateway between the source server 220, the microcircuit 100 and the playback device 214. The

  device 214 and microcircuit 100 can possibly identify themselves

  proud, for example by exchanging certificates containing random data

  tories. They can also exchange keys with each other to communicate

to quantify.

  Client application software 211 transmits signed commands and

  encrypted in microcircuit 100 by attaching the blocks to it. Of course, the mid-

  crocircuit accepts these orders only if they have been properly

signed and authenticated.

  The microcircuit calculates the signature of the block and checks the conditions of access.

  especially the fact that the user has the right to copy the content

  naked and that he has paid the reading rights. For this, he uses the access ticket he received following payment, with the rules

  that have been tattooed or included in valuable content.

  If all the conditions are well respected, the microcircuit decrypts the stream A, possibly re-encrypts it with a key associated with the playback device and transmits this content to the device 213, which can then store this multimedia content, from which the playback will be performed later . In the case where the user attempts to transfer the downloaded content to another storage means, the microcircuit 100 will only authorize the copying for content for which he has access rights, unless it is

  content marked "royalty free". In case the rights are pre-

  smells, there is in principle no copy, since the content is already

  stored on the storage device of the user's device.

Claims (13)

  1. A method of processing an information flow by a security microcircuit (100), in particular a smart card microcircuit, this microcircuit cooperating with an external device (200) capable of producing the information flow.   digital data and to use this flow of information   after treatment with the microcircuit, process characterized by the following steps: a) by the external device, production of the information flow, b) by the external device, separation (110) of the incident information flow (A + B) in two distinct fractions, with a minor fraction (A) and a major fraction (B), the major fraction having a size and / or an information flow rate significantly greater than the minor fraction,   c) transmission (120) of the minor fraction of the external device to the mid   1 5 crocircuit, d) within the microcircuit, safe treatment (130, 135) of the minor fraction, e) transmission (140) of the treated minor fraction (A ') of the microcircuit to the external device, f) by the external device , recombination (150) of the minor fraction processed (A ') with the major fraction (B) so as to produce an outgoing information flow (A' + B), g) by the external device, use (160) of the outgoing information flow (A '+ B).   2. The method of claim 1, in which the security processing of step d) is a processing of the group comprising: decryption or encryption of the stream; control or generation of a certificate or electronic signature of the flow; encoding or decoding of auxiliary information   tattooed in the stream; extracting or adding information to the flow by de-   multiplexing or multiplexing; flow validity check; management of rights to use flow information; and combination of two or   many of the previous treatments.   3. The method of claim 1 or 2, wherein: - the external device comprises a source device (220) and a device   separate user (210), the microcircuit (100) cooperating with the device   user reil (210); - steps a) and b) are implemented in the source device; and   - step f) is implemented in the user device.   4. The method of one of claims 1 to 3, wherein, after the step   eg b) of separation and before step c) of transmission, provision is made for   step (115) of processing, in particular encryption, of the mid-fraction   neure (A) by the external device, step d) of safe treatment put   implemented within the microcircuit being a step of a symmetrical treatment   that, in particular a decryption step (130).   5. The method of claim 4, wherein the security processing of step d) includes a key transcoding, comprising a decryption   with a first key then a re-encryption with a second key.   6. The method of one of claims 1 to 5, wherein the separation   of step b) comprises a temporal separation, operated by cutting   of the incident flow in time intervals.   7. The method of one of claims 1 to 6, wherein the separation   of step b) comprises a separation according to the informational content of the data composing the incident flow, operated by extraction of fields   data of a predetermined nature.   8. The method of one of claims 1 to 7, wherein the separation   of step b) is a separation which is both temporal and a function of the content   informational of the data composing the incident flow, operated by   cutting the incident flow in time intervals and extracting fields   data of a predetermined nature.   9. The method of one of claims 1 to 8, wherein the separation   of step b) and / or the safe treatment (130, 135) is a function of pa-   rameters influencing the perceptibility of separation and / or treatment and   selected in order to reduce their perceptibility.   10. The method of one of claims 1 to 9, wherein the process-   safe step d) also includes the production of a key   able to allow the decryption of the major fraction (B) by the provision external sitive.   11. The method of one of claims 1 to 10, wherein the size   and / or the information rate of the minor fraction (A) is less than % of total flow (A + B).   12. The method of claim 11, wherein the size and / or the information rate of the minor fraction (A) is between 5% and 1% of the total flow (A + B).   13. The method of claim 11, wherein the size and / or information rate of the minor fraction (A) is less than 1% of the total flow (A + B).