Digital Signatures and Digital Certificates
Summary
TLDRThis script explains digital signatures using the concept of asymmetric key cryptography. It illustrates the process of creating a hash value using SHA-256, encrypting it with the sender's private key, and embedding it in the document. The recipient uses the sender's public key to decrypt and verify the hash, ensuring document integrity. The script also introduces digital certificates, issued by certification authorities, to authenticate the sender's identity, making digital signatures legally binding and crucial for secure online transactions.
Takeaways
- π Digital signatures use asymmetric key cryptography, where a pair of mathematically related keys is used for encryption and decryption.
- π Asymmetric keys consist of a public key for encryption and a private key for decryption, ensuring that only the intended recipient can decrypt the message.
- πΌ The public key can be shared openly without compromising security, while the private key must remain confidential.
- π Digital signatures are essential for verifying the authenticity and integrity of documents, ensuring they have not been tampered with.
- ποΈ A digital signature involves creating a hash of the document using an algorithm like SHA-256, which is then encrypted with the sender's private key.
- ποΈ The encrypted hash (digital signature) is embedded in the document, which can then be sent to the recipient.
- π Upon receipt, the recipient uses the sender's public key to decrypt the hash and recalculates the hash from the document's content to verify its integrity.
- π‘οΈ Digital certificates, issued by trusted certification authorities, vouch for the sender's identity and contain a public key, adding a layer of trust to digital signatures.
- π¦ The Electronic Communications Act of 2000 in the UK made digital signatures legally binding, facilitating secure online transactions and the rise of cryptocurrencies.
- π Cryptocurrencies like Bitcoin rely on digital signatures for secure transactions, where the list of transactions is updated and verified through cryptographic means.
Q & A
What is the fundamental concept behind symmetric key cryptography?
-Symmetric key cryptography uses a single key for both encryption and decryption. The same key must be kept secret and shared between the communicating parties.
How does asymmetric key cryptography differ from symmetric key cryptography?
-Asymmetric key cryptography uses a pair of mathematically related keys: a public key for encryption and a private key for decryption. The public key can be shared openly, while the private key must be kept secret.
Why is it crucial that the private key in asymmetric cryptography is kept secret?
-The private key must be kept secret because if it falls into the wrong hands, anyone could decrypt messages intended for the key owner, compromising the security of the communication.
What role does the public key play in the process of digital signatures?
-In digital signatures, the public key is used to verify the authenticity of the signature. It can decrypt the hash value that was encrypted with the sender's private key, ensuring that the document was indeed sent by the claimed sender.
Why are digital signatures necessary in digital communication?
-Digital signatures are necessary to ensure the authenticity and integrity of a document. They provide proof that the document was sent by the claimed sender and has not been altered since it was signed.
How does the hashing process using SHA-256 contribute to the security of digital signatures?
-SHA-256 contributes to the security of digital signatures by creating a unique hash value from the document's content. Any change in the document would result in a different hash value, thus detecting tampering.
What is a digital certificate and what is its purpose in the context of digital signatures?
-A digital certificate is a file issued by a certification authority that contains the public key of the certificate holder along with other identifying information. Its purpose is to guarantee the identity of the public key owner, thus enhancing the trust in digital signatures.
How does a certification authority verify the identity of an individual applying for a digital certificate?
-A certification authority verifies the identity of an individual by requiring them to provide various details about themselves during the application process. The authority then checks these details to confirm the applicant's identity.
What is the Electronic Communications Act, and how does it relate to digital signatures?
-The Electronic Communications Act is a UK law passed in 2000 that made digital signatures legally binding. This legislation has allowed businesses to conduct transactions and sign agreements digitally with the same legal force as handwritten signatures.
How do digital signatures contribute to the security of cryptocurrencies?
-Digital signatures are fundamental to the security of cryptocurrencies as they ensure the authenticity of transactions. They verify that transactions come from the rightful owner of the cryptocurrency and have not been tampered with.
Outlines
π Asymmetric Key Cryptography and Digital Signatures
This paragraph introduces the concept of digital signatures and their reliance on asymmetric key cryptography. It explains the process of encryption and decryption using a pair of mathematically related keys, where one key encrypts the message and the other decrypts it. The example of Albert and Sheila illustrates how one person can send a secret message to another using public and private keys. The paragraph also discusses the importance of asymmetric keys in digital signatures, where the choice of which key is public or private is flexible, enabling the creation of a digital signature. It sets the stage for understanding why digital signatures are necessary by presenting a scenario where Carol and Bob have a dispute over a contract, highlighting the need for a secure and verifiable way to prove the authenticity of documents.
π The Process of Digital Signatures
This paragraph delves into the technical process of creating a digital signature. It explains how a document's content is hashed using an algorithm like SHA-256 to create a unique digest or hash value. This hash value is then encrypted with the sender's private key to form the digital signature, which is embedded in the document. The recipient can decrypt this signature using the sender's public key to verify its origin. The paragraph also emphasizes the importance of digital certificates, which are issued by trusted certification authorities to guarantee the sender's identity and the authenticity of the public key. It discusses how the recipient can use the digital certificate to ensure they are communicating with the correct person, and how the Electronic Communications Act in the UK made digital signatures legally binding, facilitating business transactions online.
π Summary of Digital Signatures and Certificates
The final paragraph summarizes the key points about digital signatures and certificates. It reiterates that digital signatures use asymmetric key cryptography to ensure the integrity and authenticity of documents. The process involves hashing the document's content to create a digest, encrypting this digest with the sender's private key, and embedding it into the document. The recipient then decrypts the digest using the sender's public key and recalculates the hash to verify the document's integrity. The paragraph also explains the role of digital certificates, which are issued by certification authorities to guarantee the sender's identity and the validity of the public key. It concludes by emphasizing the importance of digital signatures in secure communication and the legal recognition of their binding nature.
Mindmap
Keywords
π‘Digital Signatures
π‘Symmetric Key Cryptography
π‘Asymmetric Key Cryptography
π‘Public Key
π‘Private Key
π‘Hash Function
π‘Digital Certificate
π‘Certification Authority (CA)
π‘Cryptographic Hash
π‘SHA-256
Highlights
Digital signatures utilize asymmetric key cryptography, which involves a pair of mathematically related keys.
In asymmetric cryptography, one key encrypts data that can only be decrypted by the other key.
A public key can be shared openly, while the private key must be kept secret by its owner.
The choice of which key is public and which is private is flexible in asymmetric cryptography.
Digital signatures are essential for verifying the authenticity and integrity of digital documents.
A hash function like SHA-256 is used to create a unique digest of the document's content.
The hash value changes significantly with even the slightest alteration in the document.
The sender encrypts the hash using their private key to create a digital signature.
The digital signature is embedded in the document, which can then be sent to the recipient.
The recipient uses the sender's public key to decrypt the digital signature.
The recipient also calculates the hash of the received document to verify its integrity.
If the calculated hash matches the decrypted hash, the document is confirmed to be unaltered.
Digital certificates, issued by a trusted certification authority, guarantee the sender's identity.
A digital certificate contains the sender's public key, ensuring the recipient can trust the signature.
The Electronic Communications Act of 2000 in the UK made digital signatures legally binding.
Digital signatures are foundational for secure communication and transactions on the internet.
Cryptocurrencies like Bitcoin rely on digital signatures for secure transactions.
Transcripts
digital signatures rely on a symmetric
key cryptography so before we talk about
digital signatures let's quickly remind
ourselves how a symmetric key
cryptography
works with asymmetric key cryptography
there's a pair of mathematically related
keys if you encrypt a message with one
of the keys than the other key and only
the other key can be used to decrypt it
this is Albert and this is Sheila if
Sheila wants Albert to send her a secret
message
she needs an asymmetric a pair of keys a
computer program can generate these for
her she sends Albert a copy of one of
the keys and she keeps the other key to
herself instead of sending Albert a key
she could put a key in a public place
for him to go and fetch himself it
doesn't matter if someone else gets a
copy of the public key Albert uses the
public key to encrypt his message when
Albert has encrypted the message he
sends a Sheila the ciphertext only
Sheila can decrypt the ciphertext
because only Sheila has the matching key
the private key truth be told most
people don't need to worry about what's
really going on because the whole
process is taken care of
behind the scenes my programs built into
web browsers or email applications but
what do asymmetric keys have to do with
digital signatures well it so happens
that it doesn't matter which one of the
pair of keys is made public and which
one is kept private if you encrypt a
message with either one than the other
and only the other can be used to
decrypt it as long as she doesn't change
her mind later
Sheila can decide which one of the keys
will be private and which one will be
public this is the crucial feature of
asymmetric key cryptography that makes
digital signatures possible now let's
think about why we even need digital
signatures
this is Carol and this is Bob Bob's
builder carol has a leaky roof and she
asks Bob to fix it
Carol agrees to pay Bob a thousand
pounds to fix her roof Bob agrees to
start work on Monday and have it
finished by Wednesday
Carol writes details of the agreement on
a piece of paper and she signs it and
she sends it to Bob in the post no
computers here Bob signs the piece of
paper and sends a copy back to Carol in
the post Carol sends Bob the money bob
writes a note to carol to say he's got
the money he signs this receipt and he
sends it to Carol in the post on Monday
Bob doesn't turn up he's gone on holiday
for a week to spend the money on
Thursday it rains all day and all of
Carol's furniture is destroyed poor
Carol Carol says it's Bob's fault but
Bob denies ever having agreed to do the
work Carol takes Bob to court the judge
looks at the contract and the receipt
which Bob signed Bob is ordered to pay
the money back to Carol and to give her
some more money for new furniture and
Bob is sent to jail where he belongs
once upon a time not so long ago if you
wanted proof that a document was sent to
you by a particular person
it needed a handwritten signature on it
only written signatures were legally
binding but these days it's possible to
put a digital signature on a document
this is Jack and this is Jill Jack wants
to send a document to Jill by email no
paper this time now let's be clear
there's nothing secret about the
document neither of them care if
somebody else reads it Jill just wants
to be sure that it definitely came from
Jack and that nobody else has made any
changes to it on the way before his
document is sent some software on Jack's
computer prepares the digital signature
the purpose of this software is to
create something called a hash of the
document these days most computers do
this using an algorithm called sha-256
which was invented by the USA's National
Security Agency sha-256 takes a copy of
the document text and subjects it to a
sequence of complex mathematical
calculations and other transformations
remember as far as the computer is
concerned the document consists of
binary ones and zeros the result is
called a hash value it's also referred
to as a digest of the document the
hashing process has been designed so
that even the tiniest difference in the
original document would result in a
completely different hash value this
part of the signing process is not
encryption because the transformations
done by sha-256
are practically impossible to reverse
you can't take a hash value and use it
to work out what was in the original
document like baking a cake hashing is a
one-way process but if you were to apply
the same process to the same document
you would get exactly the same hash some
software on Jack's computer now encrypts
the hash using Jack's private key and
the encrypted hash is embedded in the
original document the document now has a
digital signature Jack sends Jill a copy
of the signed document he also sends her
a copy of the public key alternatively
he can put the public key on a website
for Jill to go and fetch Jill's computer
decrypt the digital signature using
Jack's public key if she can decrypt it
she knows it came from jack Jill's
computer then uses sha-256 to calculate
the hash value again using the text of
the document if the hash value that
Jill's computer calculates
the same as the hash value that was sent
by Jack she can be pretty sure that it
hasn't been tampered with since it was
created remember Jack and Jill really
don't care if someone else has seen the
signed document it's not a secret and it
doesn't matter if someone else gets a
hold of Jack's public key Jill simply
wants to be sure that the document was
sent by Jack of course anyone else could
have been pretending to be jack from the
start a criminal could create a fake
document hash it with sha-256 and
generate an asymmetric pair of keys
using their computer so how can Jill be
really sure that she's communicating
with jack well that's where digital
certificates come in for a fee Jack can
apply for a digital certificate to a
well known and well trusted organization
called a certification Authority
certification authorities include
companies like Verisign global sign and
Symantec to name but a few as part of
the application process
Jack's computer generates an asymmetric
pair of keys and he sends the public key
to the certification Authority along
with various details about himself
the certification Authority carefully
checks that Jack is who he says he is
then they send them a special type of
file called a digital certificate this
contains details about Jack along with
information about the certification
Authority and an expiry date bound to
this digital certificate is jack's
public key jack still has the
corresponding private key which never
left his computer Jack must of course
keep his private key safe so now when
Jack sends a signed document to Jill he
can also send her a copy of the whole
certificate or put it in a public place
for her to go and get
this means that when Jill wants to
decrypt something that Jack is encrypted
she can inspect this certificate first
and if she's happy to trust it she can
use the public key within the public key
that has been guaranteed by the
certification authority to belong to
Jack
essentially the certification authority
is vouching for Jack
needless to say applying to a
certification Authority for a digital
certificate is itself a very secure
process anything the certification
authority sent to Jack was digitally
signed by them using their own digital
certificate and this was provided by an
even higher certification authority in
the year 2000 a law was passed in the UK
called the Electronic Communications Act
this law made digital signatures legally
binding and this has allowed businesses
to thrive on the web since then we've
seen the rise of crypto currencies like
a Bitcoin a cryptocurrency is
fundamentally a secure list of who paid
who how much updating this list depends
on digital signatures to summarize
digital signatures rely on a symmetric
key cryptography a documents contents
are hashed to create a digest for
example using sha-256 the digest is
encrypted by the sender using their
private key the digest is then embedded
in the document which can be sent the
recipient decrypt the digest using the
sender's public key the recipient also
calculates a hash from the documents
contents using the same hash algorithm
if the recalculated digest matches the
decrypted digest it can be assumed that
the document hasn't been tampered with
since it was sent a digital certificate
is issued by a certification Authority
which guarantees the sender's identity
the digital certificate contains a
public key along with other information
about the sender and an expiry date
Browse More Related Video
Non-repudiation - CompTIA Security+ SY0-701 - 1.2
CompTIA Security+ Full Course: Public Key Infrastructure (PKI)
Digital Certificates Explained - How digital certificates bind owners to their public key
One Way Hash Explained
Blockchain 101 - A Visual Demo
SHA 256 | SHA 256 Algorithm Explanation | How SHA 256 Algorithm Works | Cryptography | Simplilearn
5.0 / 5 (0 votes)