it will help in cyber forensics.

1. 1
By,
Gopika Babu
1st
Year MSc. Forensic
science Lovely
Professional University

2. 2
Public key cryptography or asymmetric cryptography,
is an encryption scheme that uses two mathematically related, but not
identical, keys - a public key and a private key. Unlike symmetric key
algorithms that rely on one key to both encrypt and decrypt, each key
performs a unique function. The public key is used to encrypt and the
private key is used to decrypt.
In such a system, any person can encrypt a message using
the receiver's public key, but that encrypted message can only be
decrypted with the receiver's private key. There are many aspects to
security and many applications, ranging from secure commerce and
payments to private communications and protecting health care
information. One essential aspect for secure communications is that of
cryptography. But it is important to note that while cryptography
is necessary for secure communications, it is not by itself sufficient. The
reader is advised, then, that the topics covered here only describe the first
of many steps necessary for better security in any number of situations.

3. 3
Cryptography or cryptology is the practice and study
of techniques for secure communication in the presence of third parties
called adversaries. It is about constructing and analyzing protocols that
prevent third parties or the public from reading private messages; various
aspects in information security such as data confidentiality, data integrity,
authentication, and non-repudiation are central to modern cryptography.
There are five primary functions of cryptography:
1. Privacy/confidentiality: Ensuring that no one can read the message
except the intended receiver.
2. Authentication: The process of proving one's identity.
3. Integrity: Assuring the receiver that the received message has not been
altered in any way from the original.
4. Non-repudiation: A mechanism to prove that the sender really sent this
message.
5. Key exchange: The method by which crypto keys are shared between
sender and receiver.
In cryptography, we start with the unencrypted data,
referred to as plaintext. Plaintext is encrypted into ciphertext, which will
in turn (usually) be decrypted back into usable plaintext. The encryption
and decryption is based upon the type of cryptography scheme being
employed and some form of key. For those who like formulas, this process
is sometimes written as:
C = Ek(P)
P = Dk(C)

4. 4
where P = plaintext, C = ciphertext, E = the encryption method, D = the
decryption method, and k = the key.
There are several types of cryptography algorithms. The
main three types are:
 Secret Key Cryptography (SKC): Uses a single key for both encryption
and decryption; also called symmetric encryption. Primarily used for
privacy and confidentiality.
 Public Key Cryptography (PKC): Uses one key for encryption and
another for decryption; also called asymmetric encryption. Primarily
used for authentication, non-repudiation, and key exchange.
 Hash Functions: Uses a mathematical transformation to irreversibly
"encrypt" information, providing a digital fingerprint. Primarily used
for message integrity.
Finally, cryptographyis mostclosely associated with the development and creation
of the mathematical algorithms used to encrypt and decrypt messages,
whereas cryptanalysis is the science of analyzing and breaking encryption
schemes. Cryptology is the term referring to the broad study of secret writing, and
encompasses both cryptography and cryptanalysis.
Types of Cryptography Algorithms

5. 5
Public-key cryptography, or asymmetric cryptography,
is a cryptographic system that uses pairs of keys: public keys, which may
be disseminated widely, and private keys, which are known only to the
owner. Public key cryptography, introduced in the 1970s, is the modern
cryptographic method of communicating securely without having a
previously agreed upon secret key. Public key cryptography typically uses
a pair of keys to secure communications - a private key that is kept secret,
and a public key that can be widely distributed. You should not be able to
find one key of a pair simply by having the other. Public key cryptography
is a form of asymmetric-key cryptography, since not all parties hold the
same key.
Two of the best-known uses of public key cryptography are:
 Public key encryption, in which a message is encrypted with a
recipient's public key. The message cannot be decrypted by anyone
who does not possess the matching private key, who is thus presumed
to be the owner of that key and the person associated with the public
key. This is used in an attempt to ensure confidentiality.
 Digital signatures, in which a message is signed with the sender's
private key and can be verified by anyone who has access to the
sender's public key. This verification proves that the sender had access
to the private key, and therefore is likely to be the person associated
with the public key. This also ensures that the message has not been
tampered with, as a signature is mathematically bound to the message
it originally was made with, and verification will fail for practically
any other message, no matter how similar to the original message.

6. 6
Public Key Private Key
A type of lock used in asymmetric
encryption that is used with an
encryption algorithm to convert the
message to an unreadable form.
A type of lock used in asymmetric
encryption that is used with a
decryption algorithm to convert the
received messages back to the
original message.
Used to encrypt the message. Used to decrypt the message.
Widely distributed Kept secret
The main applications of public key cryptography:
 Digital signatures - content is digitally signed with an individual’s
private key and is verified by the individual’s public key.
Security benefits of the digital signature are:
Difference between Private key and Public key
Applications of Public key cryptography

7. 7
 Authentication – since the individual’s unique private key was used
to apply the signature, recipients can be confident that the individual
was the one to actually apply the signature
 Non-repudiation – since the individual is the only one with access
to the private key used to apply the signature, he/she cannot later
claim that it wasn’t him/her who applied the signature
 Integrity - when the signature is verified, it checks that the contents
of the document or message match what was in there when the
signature was applied. Even the slightest change to the original
document would cause this check to fail.
 Encryption - content is encrypted using an individual’s public key and
can only be decrypted with the individual’s private key.
Security benefits of encryption are:
 Confidentiality - because the content is encrypted with an
individual’s public key, it can only be decrypted with the
individual’s private key, ensuring only the intended recipient can
decrypt and view the contents
 Integrity - part of the decryption process involves verifying that the
contents of the original encrypted message and the new decrypted
match, so even the slightest change to the original content would
cause the decryption process to fail.
Public Key encryption has six ingredients:
Plaintext: This is the readable message or data that is fed into the
algorithm as input.
Encryption algorithm: The encryption algorithm performs various
transformations on the plaintext.
Public and private keys: This is a pair of keys that have been selected so
that if one is used for encryption, the other is used for decryption. The

8. 8
exact transformations performed by the algorithm depend on the public or
private key that is provided as input.
Ciphertext: This is the scrambled message produced as output. It depends
on the plaintext and the key. For a given message, two different keys will
produce two different ciphertexts.
Decryption algorithm: This algorithm accepts the ciphertext and the
matching key and produces the original plaintext.

9. 9
London terrorist attack, March 2017
On 22 March 2017 Khalid Masood killed 4 people in an attack in
Westminster in London. In the days after the attack the British intelligence
service MI5 revealed that Masood had used WhatsApp before the attack.
This was discovered by examining metadata from the service for example,
details about the times of contacts.
United States, March 2017
On March 21 2017 a US man was ordered by a judge to provide access to
his encrypted hard drive. The man has been held in prison - without charge
- for 18 months accused of possessing indecent images. After his arrest
police were able to decrypt his Mac Pro computer and found evidence to
“suggest” his external hard drive contained more indecent images.
However, they were unable to decrypt the drive. The man’s lawyers say
forcing him to decrypt the hard drive would break the 5th Amendment
(the right to avoid self-incrimination). They also say the case breaches the
6th Amendment, which guarantees a speedy trial. It is unclear whether the
man will now provide the passphrase to decrypt the hard drive.
Apple vs FBI, 2016
This is one of the more famous cases involving encryption. The FBI took
Apple to court in an attempt to force them to unlock a protected iphone.
The phone belonged to Syed Rizwan Farook, who killed 14 people in a
terrorist attack in California. The FBI wanted to search the device to find
evidence of others who may have been involved in planning the attack.
To complicate the issue, iPhones can be configured to auto-erase their
contents if an incorrect passcode is entered multiple times. The FBI sought

10. 10
to compel Apple to disable this functionality on Farook’s phone. They
also wanted Apple to remove the delay between entering passcodes
(which is designed to stop people randomly trying a large number of
different codes). Apple argued that they had no facility to perform these
tasks. They also claimed they would need to write special software to do
what the FBI wanted, and that writing this software would amount to
“compelled speech” which violates the First Amendment. Eventually the
FBI were able to access the contents of the phone with help from a third
party.
From this we can concluded that Public key algorithms are fundamental
security ingredients in modern cryptosystems, applications and protocols
assuring the confidentiality, authenticity and non-repudiability of
electronic communications and data storage.
Bibliography
 https://www.garykessler.net/library/crypto.html
 https://www.globalsign.com/en-in/ssl-information-center/what-is-
public-key-cryptography/
 https://www.itgsnews.com/encryption-ethical-issues/