Digital Signature:
o
In this example the message
is only signed and not encrypted.
1)
Alice signs a message with her private key.
2)
Bob can verify that Alice sent the message and that the message has not been
modified.
o
A digital signature is
a mathematical scheme for verifying the authenticity of digital messages or
documents.
o
A valid digital signature,
where the prerequisites are satisfied, gives a recipient very strong
reason to believe that the message was created by a known sender (authentication),
and that the message was not altered in transit.
o
Digital signatures are
commonly used for software distribution, financial transactions, contract
management software, and in other cases where it is important to detect forgery
or tampering.
o
Digital signatures are
often used to implement electronic signatures, which include any
electronic data that carries the intent of a signature, but not all
electronic signatures use digital signatures.
o
Digital signatures
employ asymmetric cryptography. In many instances they provide a layer of
validation and security to messages sent through a non-secure channel.
o
Digital signatures are
equivalent to traditional handwritten signatures in many respects, but properly
implemented digital signatures are more difficult to forge than the handwritten
type.
o
Digital signatures can also
provide non-repudiation, meaning that the signer cannot successfully claim
they did not sign a message, while also claiming their private
key remains secret.
o
Further, some non-repudiation
schemes offer a time stamp for the digital signature, so that even if the
private key is exposed, the signature is valid.
o
A digital signature scheme
typically consists of 3 algorithms;
·
A key generation algorithm
that selects a private key uniformly at random from a set
of possible private keys. The algorithm outputs the private key and a
corresponding public key.
·
A signing algorithm
that, given a message and a private key, produces a signature.
·
A signature
verifying algorithm that, given the message, public key and signature,
either accepts or rejects the message's claim to authenticity.
o
Two main properties are
required. First, the authenticity of a signature generated from a fixed message
and fixed private key can be verified by using the corresponding public key.
o
Secondly, it should be
computationally infeasible to generate a valid signature for a party without
knowing that party's private key.
o
A digital signature is an
authentication mechanism that enables the creator of the message to attach a code
that acts as a signature. The Digital Signature Algorithm (DSA),
developed by the National Institute of Standards and Technology, is one
of many examples of a signing algorithm.
Below
are some common reasons for applying a digital signature to communications:
Authentication
Digital signatures can be used to
authenticate the source of messages. When ownership of a digital signature
secret key is bound to a specific user, a valid signature shows that the
message was sent by that user.
Integrity
In many scenarios, the sender and receiver of
a message may have a need for confidence that the message has not been altered
during transmission. However, if a message is digitally signed, any change in
the message after signature invalidates the signature. Furthermore, there is no
efficient way to modify a message and its signature to produce a new message
with a valid signature, because this is still considered to be computationally
infeasible by most cryptographic hash functions.
Non-repudiation
By
this property, an entity that has signed some information cannot at a later
time deny having signed it. Similarly, access to the public key only does not
enable a fraudulent party to fake a valid signature.
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