Le 50hz peut vous trahir
Publié : 21 déc. 2021 10:50
A savoir que l'on peut à présent dater les enregistrements audio/video à partir des dérives du 50hz dans le réseau électrique. (Video en anglais)
Forum des collectionneurs et utilisateurs d'ordinateurs anciens
https://www.forum.system-cfg.com/
Voici quelques articles scientifiques sur le sujet. Le 1er est celui du Dr Cooper (expert de police judiciaire à Londres) qui explique ce qu'il fait:bbc a écrit :Recently, Dr Cooper was called as a witness on ENF in court for the first time.
A gang were accused of selling weapons, and undercover police had recorded an arms deal. But the defence claimed that the police had tampered with the recording and had edited together several separate recordings together to make their case.
Dr Cooper said: "The defence made the allegations and we were asked if we could authenticate the recordings.
"We carried out various forms of analysis, including the mains hum frequency analysis and we found some good quality signals, and that the alleged date and times of the recordings matched with the extracted data from the recordings themselves."
The analysis revealed that the recordings had not been tampered with - and this proved crucial to the trial. The trio - Hume Bent, Carlos Moncrieffe and Christopher McKenzie - were found guilty and jailed for a total of 33 years for being involved in the supply of firearms.
The Electric Network Frequency (ENF) as an Aid to Authenticating Forensic Digital Audio Recordings — an Automated Approach a écrit :
A recent forensic technique developed to establish the authenticity of recorded digital audio evidence is the Electric Network Frequency (ENF) Criterion. This paper confirms the applicability of the ENF criterion for use in mainland UK and introduces an automated approach to matching ENF estimates taken from a questioned recording to a database of ENF values. The signal processing procedures described have been used successfully by the Metropolitan Police Forensic Audio Laboratory in London to extract and match ENF data from evidential recordings.
Applications of ENF criterion in forensic audio, video, computer and telecommunication analysis a écrit :
This article reports on the electric network frequency criterion as a means of assessing the integrity of digital audio/video evidence and forensic IT and telecommunication analysis. A brief description is given to different ENF types and phenomena that determine ENF variations. In most situations, to reach a non-authenticity opinion, the visual inspection of spectrograms and comparison with an ENF database are enough. A more detailed investigation, in the time domain, requires short time windows measurements and analyses. The stability of the ENF over geographical distances has been established by comparison of synchronized recordings made at different locations on the same network. Real cases are presented, in which the ENF criterion was used to investigate audio and video files created with secret surveillance systems, a digitized audio/video recording and a TV broadcasted reportage. By applying the ENF Criterion in forensic audio/video analysis, one can determine whether and where a digital recording has been edited, establish whether it was made at the time claimed, and identify the time and date of the registering operation.
Applications of ENF Analysis in Forensic Authentication of Digital Audio and Video Recordings a écrit :
The electric network frequency (ENF) method is presented as a means of assessing the integrity of digital audio/video evidence. A brief description is given of different ENF types, of phenomena that determine ENF variations, analysis methods, stability within different geographical locations in continental Europe, interlaboratory validation tests, measurement uncertainties, real-case investigations, different effects of compression algorithms on ENF values, and possible problems encountered during forensic examinations. By applying the ENF method in forensic audio/video analysis, one can determine whether and where a digital recording has been edited, establish whether the recording was made at the time claimed, and identify the time and date of the registering operation.
Location Forensics Analysis Using ENF Sequences Extracted from Power and Audio Recordings a écrit :
Electrical network frequency (ENF) is the signature of a power distribution grid which represents the nominal frequency (50 or 60 Hz) of a power system network. Due to load variations in a power grid, ENF sequences experience fluctuations. These ENF variations are inherently located in a multimedia signal which is recorded close to the grid or directly from the mains power line. Therefore, a multimedia recording can be localized by analyzing the ENF sequences of that signal in absence of the concurrent power signal. In this paper, a novel approach to analyze location forensics using ENF sequences extracted from a number of power and audio recordings is proposed. The digital recordings are collected from different grid locations around the world. Potential feature components are determined from the ENF sequences. Then, a multi-class support vector machine (SVM) classification model is developed to validate the location authenticity of the recordings. The performance assessments affirm the efficacy of the presented work.
abstract a écrit :Applications of ENF Analysis in Forensic Authentication of Digital Audio and Video Recordings
Small frequency variations in the electrical power network, which are the same through the area serviced by the network, can be used to assess the integrity of audio and video evidence. Small amounts of hum usually leak into a recording, and this provides a unique time signature. By archiving power line frequencies over many years, the time of a recording can be determined by comparing it to the information in the archive database. Similarly, discontinuities in hum frequency or multiple frequency components provide additional forensic evidence.
ENF analysis on recaptured audio recordings a écrit :
Electric Network Frequency (ENF) based forensic analysis is a promising tool for timestamp authentication and forgery detection in such multimedia recordings as audios and videos. ENF signal is embedded in an audio recording due to electromagnetic interference from the power lines. The time of creation of a multimedia recording can be determined by comparing the ENF signal embedded in the recording with a reference ENF database collected from the power grid. In this paper, we conduct a study of the effect of recapturing of audio recordings on the ENF embedding. We demonstrate that recaptured audio recordings pick up two ENF signals: the content ENF signal which is inherited from the original audio recording; and the recapturing ENF signal which is embedded from the recapturing process. Conventional ENF signal extraction techniques on such recordings may fail when the two ENF signals are at the same nominal value. A decorrelation algorithm is proposed to extract the content ENF signal and the recapturing ENF signal. The experimental results show the effectiveness of the proposed method in the estimation of both the ENF signals.
Une vidéo anglaise qui parle d'un truc en France serait étonnant en effet. Un truc technique utilisé encore plus. Car il n'y a pas que dans le domaine des voitures électriques qu'on est à la ramasse des pays civilisés. (Bah on est plus passionnés de débats politiques stériles sur la société que de de vrais progrès techniques ou technologiques). Du reste je ne sais pas si comme en Angleterre (ou en Suisse), RTE publie la dérive du 50hz. Mais comme la défense est libre chez nous, cette technique pourrait parfaitement être utilisée si RTE publiait autre chose que du blabla.Donc pas dans un cadre juridique français si je comprends bien.