Quaternion-based Encryption/Decryption of Audio Signal Using Digital Image as Variable Key

With the rapid growth of communication technology, cryptography plays a significant role in securing and verification of information exchanged via public communication channels.   The current paper introduces a novel method for encrypting/decrypting audio signal using a selected digital image as a complicated key and cover for audio signal.  Each sample of the audio signal is combined with the values of the three color components of a pixel fetched from the cover image yielding a quaternion number.   The absolute value of this quaternion number is then transmitted and when received, the original value of the audio sample can be extracted using simple quaternion mathematics. A second level of complexity can be added to this approach by applying one of the well-known cryptographic techniques (symmetric or asymmetric).   The suggested approach is implemented using Matlab simulation software and the generated audio signal is compared with the original one using some performance metrics.  The obtained results show that the proposed approach is robust and more secure against cryptanalysis attacks

A New Scheme for Spreading & De-spreading in the Direct Sequence Spread Spectrum Mechanism

Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS) techniques are widely used to implement code-division multiple access (CDMA) in wireless communication systems.  Both DSSS and FHSS systems help reducing the effects of interference on the transmitted information making it robust against channel impairments.  DSSS uses a signal bandwidth that is much broader than the information signal bandwidth.  Traditionally, the wide band signal is generated by multiplying the narrowband information signal with a binary code, often designated as a spreading code, to generate the wideband signal that is transmitted. The original information signal can be recreated at the receiver by multiplying the received wideband signal by the same binary code (now designated as a de-spreading code) used to generate the wideband transmitted signal.  To extract the original information signal, the spreading and de-spreading codes must be in synchronism at the receiver and amplitude match with each other.  A new modification for the direct sequence spread spectrum is proposed in this paper. The mechanism introduced in this approach implicates generating the wideband signal by circularly shifting the spreading code (PN) by n places, where n represents the value of the current byte of information signal. The yielded signal is modulated using BPSK modulator before transmitting it.  The original information signal is extracted at the receiver by correlating the received signal (which is actually the original spread sequence circularly shifted by n places) with a locally generated replica of the spreading code.  The position of the maximum value of the cross-correlation vector represents the value of the information signal byte.  The proposed configuration has been implemented using Simulink simulator and the obtained results show that its performance is identical with the conventional DSSS

Using Quaternion Fourier Transform in Steganography Systems

steganography is the discipline of exchanging information messages in such way that no one, other than the intended recipient, suspects the existence of the message.  The transmitted message can be in textual or multimedia form (audio, image or video) and can be hidden within cover media. Moreover, the hidden message can be in either plain or cipher form.  In steganography, the majority of hiding techniques are implemented either in spatial domain or in frequency domain of the cover media.   The current contribution introduces a new a steganography technique for hiding a textual message within a cover image.   Both the message and the cover image is converted to quaternion form and then only the quaternion message is converted to the frequency domain using Quaternion Fast Fourier Discrete Transform (QFFDT) technique.  Simple quaternion mathematics are used to combine the message (in quaternion frequency domain) within the cover image (in quaternion form).  Conversely, the hidden message can be revealed at the receiver using simple quaternion mathematics in presence of the original cover image.  The proposed method allows hiding a huge amount of data and it is much complicated against steganalysis compared to the traditional methods. The method is assessed using the known performance metrics and the obtained results show that it is robust and more secure against steganalysis attacks without affecting the consumed bandwidth of the communication channel

Synthesis and characterization of new chromeno[2,3-b]pyridines via the Friedländer reactions of 8-allyl-2-amino-4-oxo-4H-chromene-3-carboxaldehyde

New series of chromeno[2,3-b]pyridines, 2-8, have been obtained from 1,8-diazabicyclo [5.4.0]undec-7-ene catalyzed Friedländer reaction of 8-allyl-2-aminochromone-3-carboxaldehyde (1) with some carbonyl compounds containing a reactive α-methyl or methylene group namely 2-acetylthiophene, 3-acetylpyridine, 4-chloroacetophenone, 4,6-diacetylresorcinol, acetylacetone, dibenzoyl methane and acetoacetanilide. Heteroannulated chromones, 13-16, were prepared from Friedländer reaction of 1 with some cyclic α-methylene ketones namely 2-phenyliminothiazolidin-4-one, pyrazoline-3,5-dione, 5,5-dimethylcyclohexane-1,3-dione and thiobarbituric acid. Structures of the newly synthesized compounds have been established from elemental analysis and spectroscopic data

An investigation of teachers\u27 self-reported and actual written feedback practices in Egyptian ESL Classes

There have been ongoing investigations on whether providing corrective feedback on grammatical errors in L2 writing is effective or not since the debate first emerged between Truscott (1996) and Ferris (1999). Research has focused mainly on students\u27 performances and preferences as well as teachers\u27 perceptions and beliefs regarding error correction. However, limited research has compared teachers\u27 actual practices to their self-reported practices. Therefore, this study focused on written feedback practices in a university context in Egypt, where the researcher investigated how teachers actually corrected grammatical errors as compared to what they reported in the survey. The major error correction strategies used in this study were related to two categories: comprehensiveness (comprehensive and selective correction) and explicitness (direct, indirect coded, and indirect un-coded correction). Data were gathered using three instruments: (1) a survey filled out by 65 teachers, (2) written feedback samples collected from 13 teachers, and (3) follow-up interviews conducted with seven teachers. The teachers who participated in this study work at The School of Continuing Education at The American University in Cairo. Teachers’ responses to the survey were compared to their actual practices in the feedback samples they provided. The results indicated that there were various differences between the teachers\u27 actual and self-reported practices, such as over-reported, under-reported, or contrasting reported practices. The researcher conducted follow-up interviews to have an in-depth investigation of the reasons for the differences found. The study showed that teachers tended to over-report their comprehensiveness practices and under-report their explicitness practices. In addition, the reported practices showed that the majority prefer using comprehensive, selective, and indirect coded corrections, while they actually practiced comprehensive and direct corrections. Possible implications were discussed regarding ways to minimize the differences between teachers\u27 self-reported and actual practices, as well as suggestions for providing effective corrective feedback to L2 students\u27 writing