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Abstract:The Convertible Authentication Encryption (CAE) scheme, allows the signer to generate an authentic ciphertext signature, which can be recuperated and validated by a specific recipient only. In case of any kind of dispute the recipient is capable enough to convert the ciphertext signature as a normal signature and that can be validated publicly. The CAE schemes are used for transformation of confidential information over insecure networks, because they provide confidentiality, authenticity and integrity for the transmitted message or information. We propose a new CAE scheme by integrating the concepts of ECC-based self-certified public keys and encryption scheme. The security analysis shows that the proposed CAE scheme fulfill the basic security conditions such as indistinguishability of ciphertext signature, unforgeability and nonrepudiation. The performance analysis shows that our proposed CAE scheme has little advantage over Wu and Lin scheme regarding computational complexity and timings.

In a proxy blind signature scheme, there is an integration of the properties as well as advantages of both signature schemes namely proxy signature and blind signature. The concept of this signature scheme with a salient feature that, it allows a designated person say proxy signer to sign on behalf of original signer, in such a way that he/she neither has any idea about the content of the message, nor he/she can make a linkage between the signature and the identity of the requester. Therefore, it is very suitable and easily adoptable for electronic commerce, e-cash applications. Recently, Pradhan and Mohapatra et al.’s claims that their proposed signature scheme satisfies all the properties mandatory for a proxy blind signature scheme. Unfortunately, their scheme fails to fulfil the unlinkability property. To overcome with this weakness, an improved proxy blind signature scheme is presented with the same intractable problem ECDLP. The analysis shows that the new scheme resolves the problem in the former scheme and meets all the aspects of security features needed by proxy blind signature scheme. The analytic results prove that the new scheme is more secure and practicable.