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Asymmetric cryptography, also known as public key cryptography, uses public and private keys to encrypt and decrypt data. The keys are simply large numbers that have been paired together but are not identical (asymmetric). One key in the pair can be shared with everyone; it is called the public key. The other key in the pair is kept secret; it is called the private key. Either of the keys can be used to encrypt a message; the opposite key from the one used to encrypt the message is used for decryption.

ADVANTAGES
• A symmetric cryptosystem is faster.
• In Symmetric Cryptosystems, encrypted data can be transferred on the link even if there is a possibility that the data will be intercepted. Since there is no key transmiited with the data, the chances of data being decrypted are null.
• A symmetric cryptosystem uses password authentication to prove the receiver’s identity.
• A system only which possesses the secret key can decrypt a message.

DISADVANTAGES
• Symmetric cryptosystems have a problem of key transportation. The secret key is to be transmitted to the receiving system before the actual message is to be transmitted. Every means of electronic communication is insecure as it is impossible to guarantee that no one will be able to tap communication channels. So the only secure way of exchanging keys would be exchanging them personally. • Cannot provide digital signatures that cannot be repudiated

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In a public key encryption system, any person can encrypt a message using the receiver's public key. That encrypted message can only be decrypted with the receiver's private key. To be practical, the generation of a public and private key -pair must be computationally economical. The strength of a public key cryptography system relies on the computational effort (work factor in cryptography) required to find the private key from its paired public key. If so, effective security only requires keeping the private key private; the public key can be openly distributed without compromising security.

Strengths
The asymmetric nature of public-key cryptography allows it a sizable advantage over symmetric-key algorithms. The unique private and public keys provided to each user allow them to conduct secure exchanges of information without first needing to devise some way to secretly swap keys. This glaring weakness of secret-key cryptography becomes a crucial strength of public-key encryption.

Weaknesses
Keys in public-key cryptography, due to their unique nature, are more computationally costly than their counterparts in secret-key cryptography. Asymmetric keys must be many times longer than keys in secret-cryptography in order to boast equivalent security. Keys in asymmetric cryptography are also more vulnerable to brute force attacks than in secret-key cryptography. There exist algorithms for public-key cryptography that allow attackers to crack private keys faster than a brute force method would require. The widely used and pioneering RSA algorithm has such an algorithm that leaves it susceptible to attacks in less than brute force time. While generating longer keys in other algorithms will usually prevent a brute force attack from succeeding in any meaningful length of time, these computations become more computationally intensive. These longer keys can still vary in effectiveness depending on the computing power available to an attacker.

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Public key ( asymmetric ) encryption work
For asymmetric encryption to deliver confidentiality, integrity, authenticity and non-repudiability, users and systems need to be certain that a public key is authentic, that it belongs to the person or entity claimed and that it has not been tampered with or replaced by a malicious third party.

Strengths of Public Key
An important advantage of asymmetric ciphers over symmetric ciphers is that no secret channel is necessary for the exchange of the public key. The receiver needs only to be assured of the authenticity of the public key. Symmetric ciphers require a secret channel to send the secret key in order to generate at one side of the communication channel to the other side.

Weaknesses of Public Key
A disadvantage of asymmetric ciphers is that they tend to be about "1000 times slower." By that, I mean that it can take about 1000 times more CPU time to process an asymmetric encryption or decryption than a symmetric encryption or decryption.

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The public key encryption is also called as asymmetric key encryption, which is used to encrypt or decrypt data while transmission. It uses two different keys to encrypt and decrypt the data.

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The public key encryption is also called as asymmetric key encryption, which is used to encrypt or decrypt data while transmission. It uses two different keys to encrypt and decrypt the data.

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STRENGHTS

1. It allows message authentication.
As public key encryption allows using digital signatures, message recipients will be able to verify messages to be truly coming from a particular sender.

2. It is convenient.
Asymmetric encryption solves the problem of distributing keys for encryption, with everyone publishing their public keys, while private keys being kept secret.

3. It allows for non-repudiation.
Digitally signed messages are like physically signed documents. Basically, it is like acknowledging a message, and therefore, the sender will not be able to deny it.

WEAKNESSES

1. It is a slow process.
Public key encryption in this method is slow compared with symmetric encryption, which means that it is not suitable for decrypting bulk messages.

2. Its public keys are not authenticated.
Basically, no one absolutely knows that a public key belongs to the individual it specifies, which means that users will have to verify that their public keys truly belong to them.

3. It risks loss of private key, which may be irreparable.
When you lose your private key, your received messages will not be decrypted.

CHONG JIA NING 1141327463

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Public Key is made available to everyone via a publicly accessible repository or directory.  To decode an encrypted message, a computer must use the public key, provided by the originating computer, and its own private key.

Strenghts:

Provides stronger identity checking through secret private keys.

Non-interactive login is possible.

Provide a method for digital signatures

Weakness:

Not secure since the public key used for encryption is published and available to anyone

Distribution of public keys can be cumbersome in large environments and cause not scalable

Slower speed

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In a public key encryption system, any person can encrypt a message using the receiver's public key. That encrypted message can only be encrypted with the receiver's private key. To be practical, the generation of a public and private key -pair must be computationally economical.
The strength of a public key cryptography system relies on the computational effort (work factor in cryptography) required to find the private key from its paired public key. If so, effective security only requires keeping the private key private; the public key can be openly distributed without compromising security .
The weaknesses is among symmetric key encryption algorithms, only the one-time pad can be proven to be secure against any adversary – no matter how much computing power is available. However, there is no public key scheme with this property, since all public key schemes are susceptible to a "brute-force key search attack". Such attacks are impractical if the amount of computation needed to succeed – termed the "work factor" by Claude Shannon – is out of reach of all potential attackers. In many cases, the work factor can be increased by simply choosing a longer key.

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Asymmetrical encryption is also known as public key cryptography, which is a relatively new method, compared to symmetric encryption. Asymmetric encryption uses two keys to encrypt a plain text. Secret keys are exchanged over the Internet or a large network. It ensures that malicious persons do not misuse the keys. It is important to note that anyone with a secret key can decrypt the message and this is why asymmetrical encryption uses two related keys to boosting security. A public key is made freely available to anyone who might want to send you a message. The second private key is kept a secret so that you can only know.A message that is encrypted using a public key can only be decrypted using a private key, while also, a message encrypted using a private key can be decrypted using a public key. Security of the public key is not required because it is publicly available and can be passed over the internet. Asymmetric key has a far better power in ensuring the security of information transmitted during communication.