Hashing is a cryptographic technique essential for data integrity, authenticity, and non-repudiation, generating unique fixed-size hash values from input data. It is widely used in applications like password storage and digital signatures, with well-known algorithms including SHA-256 and Argon2. Digital signatures use hashing to ensure sender authenticity and document integrity, relying on public key infrastructure for verification.

1. Hashing
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• Hashingis a cryptographic techniques used in
information security to ensure data integrity,
authenticity, and non-repudiation.
• Hashing is a process of taking input data and generating a fixed-
size string of characters, known as a hash value or digest.
• The hash function takes the input data and applies a
mathematical algorithm to produce the hash value, which is
unique to the input data.

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• Hash functions are designed to be one-way,
meaning it is computationally infeasible to derive the
original input data from the hash value.
• Hashing is commonly used for various purposes, such as
password storage, data integrity, verification, and
digital forensics.

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• It allows for quick and efficient comparison of data
without revealing the original content.
• Key characteristics of hashing include:

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• 1- One-Way Function: Hash functions are designed to be
one-way, meaning it is computationally infeasible to
reverse-engineer the original input data from the hash
value.
• Given the same input, the hash function will always produce the
same hash value.

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• 2- Fixed Output Size: Hash functions
generate a fixed-length hash value, regardless
of the size of the input data.
• For example, the SHA-256 hash function produces a 256-bit
(32-byte) hash value.

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• 4- Collision Resistance: A good hash function should
have a low probability of producing the same hash
value for different input data.
• This property is known as collision resistance and ensures
that it is highly unlikely (uncommon) for two different inputs
to produce the same hash value.

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• 5- Wide Range of Applications: Hashing has numerous
applications/ usage in information security.
• Some common uses include password storage (storing
hashed passwords instead of plaintext), data integrity
checking, digital signatures, checksums, and data
fingerprinting.

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• Popular hash functions include MD5 (Message Digest 5),
SHA-1 (Secure Hash Algorithm 1), and SHA-256 (Secure
Hash Algorithm 256- bit).
• However, it's important to note that older hash functions like
MD5 and SHA-1 are considered weak and are not
recommended for security-critical applications due to known
vulnerabilities.

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• Popular hash functions include MD5 (Message Digest 5),
SHA-1 (Secure Hash Algorithm 1), and SHA-256 (Secure
Hash Algorithm 256- bit).
• However, it's important to note that older hash functions like
MD5 and SHA-1 are considered weak and are not
recommended for security-critical applications due to known
vulnerabilities.

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• Thereare severalpowerful hashingalgorithmsused in
information security to ensure the integrity and security of
data.
• Here are some notable examples:

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• SHA-256 (Secure Hash Algorithm 256-bit): It is a
widely used cryptographic hash function that belongs to
the SHA-2 family (SHA- 224, SHA-256, SHA-384, SHA-512,
SHA-512/224, and SHA-512/256).
• It generates a 256-bit hash value and is known for its
resistance to cryptographic attacks.

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• SHA-512: SHA-512 is considered the strongest hashing
algorithm in terms of its cryptographic strength and
resistance to brute-force attacks, also belongs to SHA-2
family.
• It generates a 512-bit hash value, which provides a larger
output size compared to other algorithms in the SHA-2
family.

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• SHA-3(Secure Hash Algorithm 3): It is the
latest member of the Secure Hash Algorithm
family.
• It includes hash functions such as SHA-3-224, SHA-3-256,
SHA-3-384, and SHA-3-512.
• SHA-3 algorithms are designed to
provide better resistance against

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• Argon2:It is a memory-hard hashing algorithm that won the
Password Hashing Competition in 2015.
• It is designedto be resistantagainstGPU-based attacks
and offers strong security for password hashing applications.

15. Digital Signatures
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• Digital signatures are cryptographic mechanisms used to
provide authenticity, integrity, and non-repudiation of
digital documents or messages.
• They ensure that the sender of the message is
verified, and any
alterations to the message can be detected.
• Here are some key points about digital signatures:

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• 1- Authentication: Digital signatures verify the identity of the
sender or signer of a digital document.
• They use public key cryptography to associatea unique
digital signature with the signer's identity.
• The recipient can use the correspondingpublic key to verify the
signature and confirm the authenticity of the sender.

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• 2- Integrity: Digital signatures ensure the integrity of the digital
document by detecting any modifications or tampering.
• The signatureis calculatedbasedon the content of the document,
and even a small change in the document will result in a different
signature.
• This allows the recipient to verify that the document has not been
altered since it was signed.

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• 3- Non-Repudiation: Digital signatures provide non-
repudiation, meaning the signer (sender) cannot deny their
involvement in signing the document.
• The recipient (receiver) can prove the authenticity of the
signature and the document, preventing the signer from later
claiming that they did not sign it.

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• 4- Public Key Infrastructure (PKI): Digital signatures often
rely on a public key infrastructure, where a trusted third
party, known as a Certificate Authority (CA), issues
digital certificates that bind a person's identity to their public
key.
• This enables the recipient to verify the authenticity of the
signer's public key and establish trust in the digital signature.

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• 5- Application in Document Signing and
Authentication: Digital signatures have various
applications, including secure document signing,
authentication in online transactions, secure email
communication, and software distribution.
• They provide a means to establish trust and ensure the
integrity of digital information.

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• To create a digital signature, the sender uses their private
key to encrypt a hash value of the document.
• The recipient can then use the sender's public key to
decrypt the signature and compare it with a computed hash
value of the received document.
• If the two values match, the signature is considered valid.

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• Here are some of the top secure digital signature
algorithms:
• RSA (Rivest-Shamir-Adleman): RSA is a
widely usedand established
algorithm for digital signatures.
well
-
• It offers strong security based on the difficulty of factoring
large numbers.

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• ECDSA (Elliptic Curve Digital Signature Algorithm): ECDSA
is a widely adopted digital signature algorithm that
uses elliptic curve cryptography.
• It offers strong security with shorter key lengths, making it
efficient for resource-constrained environments.

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• EdDSA (Edwards-curve Digital Signature Algorithm):
EdDSA is a modern digital signature algorithm that
provides strong security and efficient signing and
verification processes.
• It is based on elliptic curve cryptography and is gaining
popularity in various applications.

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• Schnorr Signature: Schnorr Signature is
a secure digital signature algorithm known for its
simplicity and efficiency.
• It offers strong security and has advantagesin terms of
key aggregation and multisignature schemes.

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• DSA (Digital Signature Algorithm): DSA is a widely
used digital signature algorithm, particularly in the context of
the Digital Signature Standard (DSS).
• It provides strong security when implemented correctly.

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• Digital Signatures play a crucial role in ensuring the
integrity and authenticity of digital documents, providing a
reliable mechanism for verifying the identity of the sender
and detecting any modifications to the content.