Uzamsal Alanda Bir Kripto-Stegano Hibrit Uygulama

Öz

Gelişen teknoloji ile birlikte iletişimde veri güvenliği ihtiyacı artmaktadır. Veri güvenliğini sağlamanın en iyi yolu kriptografidir. İnsanlık yüzlerce yıldır birçok kriptografi yöntemi önerdi. Günümüzde oldukça güvenli ancak yüksek işlem gücü gerektiren karmaşık şifreleme algoritmaları bulunmaktadır. Geçmişte kullanılan şifreleme teknikleri daha az güvenlidir ancak daha az işlem gücü gerektirir. Bu makale, eski bir şifreleme yöntemi olan Vigenère şifresinin geliştirilmiş bir versiyonunu önermektedir. Geliştirilmiş Vigenère şifresi ile oluşturulan şifre metni, iletim ortamında güvende tutmak için bir görüntüde de gizlenir. Gizleme işlemi, bir diğer veri güvenliği yöntemi olan steganografi ile gerçekleştirilir. Böylece hem şüpheden uzak hem de güvenli bir iletişim yöntemi ortaya çıkmıştır. Önerilen yöntemin kriptolojik güvenliği Avalanche etkisi ölçülmüş, steganografik güvenliği ise SSIM ve PSNR ölçümleri ile değerlendirilmiştir.

Anahtar Kelimeler

• Vigenère tablosu
• Vigenère şifreleme
• Steganografi
• Çığ etkisi

A Crypto-Stegano Hybrid Application on Spatial Domain

Abstract

The need for data security in communication is increasing with the developing technology. The best way to ensure data security is cryptography. Humanity has proposed many cryptography methods for hundreds of years. Today, there are complex cryptography algorithms, which are quite secure but require high processing power. Cryptography techniques used in the past are less secure but require less processing power. This article proposes an extended version of the Vigenère cipher, which is an ancient encryption method. Extended Vigenère cipher is able to encrypt upper and lower case letters, numeric characters, and punctuation marks. In addition, the method can use upper and lower case letters, numeric characters and punctuation marks as encryption key, and there is no key length limit. The cipher text generated with the extended Vigenère cipher is also hidden in an image to keep it safe in the transmission medium. Hiding is performed with LSB steganography, which is another data security method. Thus, both the readability and detectability of confidential data are reduced. The cryptological security of the proposed method is measured by the Avalanche effect. Steganographic safety is evaluated with SSIM and PSNR measurements. A user graphical interface has been developed and the maximum payload of the carrier image is measured before encryption. Proposed method applied on some test images with different specifications. 1 bit key modification avalanche effect results of proposed method with random plain texts between 1000-10000 characters with a key length of 8 and 16 characters is close to 50%. Also, SSIM value calculated over 0.99 each time while maximum steganographic payload of the test images reached.

Keywords

• Vigenère table
• Vigenère cipher
• Steganography
• Avalanche effect

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