Cryptographic tools are software or hardware utilities designed to secure data through encryption and other cryptographic methods.

1. Week#11
Lecture#01

2. Cryptographic Tools
• Cryptographic tools are software or hardware utilities designed
to secure data through encryption and other cryptographic
methods.
• They help in transforming readable data (plaintext) into an
unreadable format (ciphertext) to protect it from unauthorized
access.
These tools include:
– Encryption algorithms (e.g., AES, RSA)
– Hash functions (e.g., SHA-256, MD5)
– Cryptographic protocols (e.g., SSL/TLS, PGP)

3. Encryption Algorithms
Symmetric Encryption:
• Uses a single key for both encryption and decryption. It is fast
and suitable for encrypting large amounts of data.
• Common algorithms include:
– AES (Advanced Encryption Standard): Widely used, secure,
and efficient. It supports key sizes of 128, 192, and 256 bits.
– DES (Data Encryption Standard): Older algorithms, are
now largely considered insecure due to advances in
computational power.

4. Encryption Algorithms
• Asymmetric Encryption: Uses a pair of keys—a public
key for encryption and a private key for decryption. It
is computationally more intensive but allows secure
key exchange.
• Common algorithms include:
– RSA (Rivest-Shamir-Adleman): One of the first public-key
cryptosystems, used widely for secure data transmission.
– ECC (Elliptic Curve Cryptography): Provides similar security to
RSA but with smaller key sizes, making it more efficient.

5. Hash Functions
• SHA (Secure Hash Algorithm) family (e.g., SHA-1,
SHA-256, SHA-3): Produces a fixed-size hash value
from input data, ensuring data integrity.
• MD5 (Message Digest Algorithm 5): Now considered
outdated due to vulnerabilities, but still used in some
legacy systems.

6. Public-Key Infrastructure (PKI)
• Public-key infrastructure (PKI) is a framework used to
manage digital keys and certificates.
• PKI is fundamental for enabling secure
communications and transactions on the internet,
ensuring data integrity, authentication, and non-
repudiation.

7. Public-Key Infrastructure (PKI)
It enables secure data exchange over networks by providing:
–Public and private keys: Key pairs used for encryption and
decryption.
–Digital certificates: Issued by a trusted Certificate Authority
(CA), these certificates verify the ownership of a public key.
–Certificate Authorities (CAs): Trusted entities that issue and
cancel digital certificates.
–Registration Authorities (RAs): Entities that authenticate the
identity of users before certificates are issued.

8. Digital Certificates
• Digital certificates are electronic documents used to associate a
public key with the identity of its owner.
Components
Each certificate typically contains:
– Subject: The entity that owns the public key (e.g., a person, or
organization).
– Public Key: The public key of the subject.
– Issuer: The CA that issued the certificate.
– Serial Number: A unique identifier for the certificate.
– Validity Period: The time frame during which the certificate is valid.
– Signature: The digital signature of the CA, verifying the certificate’s
authenticity.

9. Digital Signatures
• Digital signatures are cryptographic methods used to verify
the authenticity and integrity of digital messages or
documents.
They involve:
– Creation process: The sender creates a hash of the
message and encrypts it with their private key to create a
signature.
– Verification process: The recipient decrypts the
signature with the sender’s public key and compares it to

10. Digital Signatures
Digital signatures provide:
• Authentication: Confirming the sender's identity.
• Integrity: Ensuring the message has not been
altered.
• Non-repudiation: Preventing the sender from
denying they sent the message.

11. Steganography
• Steganography involves hiding information within
other non-secret data to conceal the existence of the
message.
• Techniques include:
Image Steganography
• LSB (Least Significant Bit): Alters the least significant
bits of image pixels to embed data, making changes
invisible to the human eye.

12. Steganography
Audio Steganography
• Echo Hiding: Embeds data by altering echo signals in
audio files.
• Phase Coding: Modifies the phase of audio signals to
encode information.
Network Steganography
 Protocol Manipulation: Embeds data in unused or
optional fields within network protocol headers.

13. Steganography
Text Steganography
• Format-Based Methods: Uses changes in text
formatting (e.g., font, spacing) to hide data.
• Character-Based Methods: Introduces invisible
characters (e.g., zero-width spaces) into text to embed
information.

14. Protocols for Secure Communications
• Protocols for secure communications ensure data is
transmitted securely over networks, protecting against
eavesdropping, tampering, and other cyber threats.
 Securing Internet Communication with S-HTTP
and SSL
• The Internet was initially designed without security in mind,
leading to the later addition of security measures as threats
grew.

15. S-HTTP (Secure Hypertext Transfer Protocol):
• Purpose: Encrypts individual messages between client and
server.
• Mechanism: Each message requires a new session; the
client sends its public key, and the server generates and
encrypts a session key with it. Both then use this session
key to encrypt messages.
• Features: Provides confidentiality, authentication, and data
integrity; designed for easy integration with existing HTTP
applications.

16. Securing E-mail with S/MIME, PEM, and PGP
• Adaptations to email protocols like SMTP have incorporated
security measures to counter its inherent insecurity.
S/MIME (Secure/Multipurpose Internet Mail
Extensions):
–Purpose: Enhances MIME to secure email using digital
signatures and encryption.
–Mechanism: Uses public key cryptosystems for digital
signatures and encryption. Supports algorithms like SHA-1, RSA,
and 3DES.
–Features: Standardizes message content type, and supports
signing, encrypting, and decrypting messages.