- Nowadays data security is one of the important issues, especially for increasing transactions via the internet. This paper presents a hybrid cryptosystem using RSA (Asymmetric) and Blowfish (Symmetric) algorithm. Hybrid encryption is a combination of symmetric and asymmetric encryption methods. Symmetric algorithms are mostly used for encryption of messages than asymmetric.
INTRODUCTION
Nowadays strength of the cryptosystem cannot be totally ensured. The main goal of all cryptography algorithms is to offer the best security, but due to the fact that technology is rapidly developing proposed security systems becoming less resistant to every known or new attacks.
Both symmetric and asymmetric key algorithms have
their advantages and disadvantages. Symmetric key
algorithms are faster than asymmetric algorithms. The main
requirement is that the secret key must be shared in a secure
way. Asymmetric systems provide secure transmission of
keys, but this process needs much more time. To improve
this problem is used the hybrid algorithm, which means
using a different type of cryptosystems together [
II.
RSA
RSA is founded in 1977 is a public key cryptosystem.
RSA is an asymmetric cryptographic algorithm named after
its founders Rivest, Shamir &Adelman [
III.
Blowfish is one of the symmetric key algorithms with a
64-bit block cipher and it was developed by Bruce
Schneider [
IV.
Hybrid encryption is a method of encryption that
combines two or more encryption systems. It integrates a
combination of asymmetric and symmetric encryption to
take benefit from the strengths of each form of encryption.
These strengths of the algorithm are defined as speed and
security of this algorithm. Hybrid encryption is considered
a highly secure type of encryption as long as the public and
private keys are fully secure [
A hybrid encryption scheme is one that combines the
convenience of an asymmetric encryption scheme with the
effectiveness of the symmetric encryption scheme. There
are various advantages of the combination of encryption
methods. One is that users have the ability to communicate
through hybrid encryption. Usually, during the encryption
process, the asymmetric algorithm is slowing down the
encryption process [
Symmetric and asymmetric cryptography algorithms
have their own advantages and disadvantages. In general,
symmetric ciphers are considerably faster than asymmetric
ciphers, but require all parties to somehow share a secret
key. Also, we have to take into consideration that
asymmetric algorithms allow public key arrangements and
key exchange systems, but this slowdowns encryption
process speed [
The main goal of a hybrid cryptosystem is to generate a random key for the symmetric system and after this encrypt this key for the asymmetric system. So, we will get a secret key that will be used for encryption plaintext. During Hybrid encryption process data are transferred using unique session keys along with symmetrical encryption. The public key encryption process is implemented for random symmetric key encryption. After the receiver gets the encrypted message, the public key encryption method is used to decrypt the symmetric key. After recovering of the symmetric key, then it is used to decrypt the message.
To create a strong encryption algorithm there is a proposed combination of two encryption algorithms Blowfish and RSA. There were done experiments on proposed algorithms by terms of their encryption speed, used memory and system requirements. The programming language Java is used for implementing the encryption
In general encryption time is connected to algorithm architecture. Table 1 shows encryption and decryption results on Blowfish algorithms. Size of used key is 16 bits.
The same experiment was done on RSA system, where was used different size of plaintext. Table 2 shows used encryption time in nanoseconds.
The proposed hybrid cryptosystem works as following at first system reads plaintext and generates the secret key with RSA and public keys are generated automatically. The next step is to generate Blowfish symmetric key which will be encrypted with RSA system. This provides high security for the key because the usage of RSA algorithm decreases the decryption probability of public key. So, when we share the public key, will be shared also RSA secret key. After these steps, the plaintext is encrypted using Blowfish, because as other symmetric algorithms Blowfish is fast. The decryption process is the reverse process of the abovedescribed
There was created program, implementation for this hybrid cryptosystem on Java programming. Table 3 shows program execution results on different size plaintext. Blowfish Decryption time (Nanoseconds)
RSA + Blowfish Decryption time (nanoseconds)
This paper provides a description and comparative analyses of the new hybrid cryptosystem model. The new hybrid model combines Blowfish (symmetric) and RSA (Asymmetric) cryptosystems. The paper shows program implementation and experimental research results with java programing language. Described algorithms and hybrid models are evaluated by terms of encryption speed, memory usage, encrypted file size and ensured security level. Taking into account the time and consumption of the technical resources, Blowfish is the best one else than the other reviewed. 3 2
6 4 1 2 8 2 5 6 5 1 2 1 0 2 42 0 4 84 0 9 6 RSA Decrypted file size (KB)
RSA + Blowfish Encrypted File size (KB)
As a conducted experimental result shows provided new hybrid model is significantly faster and secure because it takes all advantages and strength of symmetric and asymmetric systems. The experiment showed the following results:
If Blowfish, RSA and Blowfish + RSA hybrid algorithms are compared according to the memory used, the highest technical resources require RSA algorithm, and Blowfish is slightly behind the Blowfish + RSA hybrid scheme.
Considering the option of encryption Blowfish keeps its initial first position and is the fastest of these systems. However, the Blowfish + RSA hybrid algorithm is far below and significantly faster than RSA. And RSA takes the longest time to encrypt and is very slow.
Observation of the decryption time parameters has shown that the Blowfish + RSA hybrid algorithm and the blowfish algorithm are almost equally fast with the decryption process and are faster than the RSA algorithm.
As an overview of the encrypted file size setting, the lowest memory needs Blowfish system, the following is Blowfish + RSA, and the RSA algorithm increases the size of an encrypted file with the highest rate.
For the future is possible to review another hybrid model of symmetric and asymmetric algorithms. It is possible to conduct a series of entropy research of the different cryptographic algorithms and the above-presented hybrid model. This will allow us to identify the sustainability of each algorithm against different types of attacks, including the frequency analysis of the encrypted text.