commit d80759906251f26182562d285cdbcf8542387487
parent 05b1525467afa189db96fc2ccd7c6e2647c13623
Author: Matyja Lukas Adam <lukas.matyja@students.bfh.ch>
Date: Thu, 6 Jun 2024 02:09:10 +0200
thesis add hash text
Diffstat:
5 files changed, 25 insertions(+), 3 deletions(-)
diff --git a/doc/thesis/bibliography.bib b/doc/thesis/bibliography.bib
@@ -45,3 +45,20 @@ keywords = {Cryptography},
url = {https://ed25519.cr.yp.to/ed25519-20110926.pdf}
}
+@article{hash2012,
+author = {Sobti, Rajeev and Ganesan, Geetha},
+year = {2012},
+month = {03},
+pages = {461 - 479},
+title = {Cryptographic Hash Functions: A Review},
+volume = {Vol 9},
+journal = {International Journal of Computer Science Issues, ISSN (Online): 1694-0814}
+}
+@online{hash-nist,
+ author = "NIST",
+ title = "Hash Functions",
+ url = "https://csrc.nist.gov/projects/hash-functions#approved-algorithms",
+ addendum = "(accessed: 06.06.2024)",
+ keywords = "hash,sha-512"
+}
+
diff --git a/doc/thesis/chapters/background/blindsign.tex b/doc/thesis/chapters/background/blindsign.tex
@@ -1,5 +1,5 @@
\section{Blind Signatures}
-The project is based on existing cryptography. One important cryptographic scheme used in the Donau is the blind signature scheme. It is an extension of digital signatures which provides privacy by allowing a user to obtain a signature for a message, without revealing the contents of the message to the signer. All cryptographic elements used by the Donau where privided by the GNU Taler libraries.
+One important cryptographic scheme used by the Donau is the blind signature scheme. It is an extension of digital signatures which provides besides authenticity and non-repudiation privacy by allowing a user to obtain a signature for a message, without revealing the contents of the message to the signer. All cryptographic elements used by the Donau where privided by the GNU Taler libraries.
This section only provides an overview of blinded signatures. Detailed information about blinded signature can be found at \url{https://taler.net/papers/cs-thesis.pdf}. Blinded signatures are the key elements to reach privacy for the donor (see chapter xx). With blinded signatures a blinded unrecognizable message was signed. Only the creator of the blinded message is able to unblind the signature and therefore to receive a valid signature for the unblinded message. The Donau system uses blinded signatures to bind the identity to a donation receipt while hiding the identity of the donor. As a result of the property of blindness, the blind signer Donau is not able to link the cleartext message with the made blind signature or the blind with the unblind signature \cite[p.12]{cryptoeprint:2019/877}. There are multiple blind signature schemes. The Donau distinguishes the following two equivalent blind signature schemes:
diff --git a/doc/thesis/chapters/background/eddsa.tex b/doc/thesis/chapters/background/eddsa.tex
@@ -1,3 +1,3 @@
\section{EdDSA Signatures}
-For normal, not blinded, signatures, the Donau uses EdDSA signatures. The Edwards-curve Digital Signature Algorithm or for short EdDSA is a scheme for digital signatures based on the twisted Edwards elliptic curves and the Schnorr signature scheme. EdDSA signatures using the curve Curve25519 are also called Ed25519. The Donau only uses Ed25519. Whether Curve25519 or the Edwards-curve, the scheme is very efficient and secure.\cite{BernsteinEd25519}
+With signatures authenticity and non-repudiation want to be achieved. In this context hashes and public key cryptography are used.\cite{hash2012} For this purpose the Donau uses EdDSA signatures. The Edwards-curve Digital Signature Algorithm or for short EdDSA is a scheme for digital signatures based on the twisted Edwards elliptic curves and the Schnorr signature scheme. EdDSA signatures using the curve Curve25519 are also called Ed25519. The Donau only uses Ed25519. Whether Curve25519 or the Edwards-curve, the scheme is very efficient and secure.\cite{BernsteinEd25519}
diff --git a/doc/thesis/chapters/background/hash.tex b/doc/thesis/chapters/background/hash.tex
@@ -1 +1,6 @@
-\section{Hash functions}
+The project is based on existing cryptography. In the following only the crucial cryptographic elements used by the Donau system are described.
+\section{Hash Functions}
+Hash functions are used to compress input values to a fixed output size. Hash function are deterministic. The same input leads to the same output. The Donau uses hash functions to compress data in order to record less data in the database or to send less data over the network. To be able to clearly recognize the corresponding data from the hash, the hash function has to second-preimage resistant or better collision resistant. With second-preimage resistance no equivalent hash for any input $x'$ to a given hash $h(x)$ with $x \neq x'$ can be found in a reasonable time. Collision resistance is the stronger assumption and even prevents to find $h(x) = h(x')$ with $x \neq x'$. A further important assumption is the Avalanche Criterion. The property defines that a small change in the hash input message leads to a substantially change in the output hash. This criteria makes it hard to guess the input even if a part of the input is known.\cite{hash2012} To protect the donor, his identity is represented as salted hash of the tax identifiaction number. The salt is a small value with high entropy to make it more difficult to guess the hashed value. \\
+
+The Donau uses the SHA-512 hash function. SHA-512 is part of the SHA-2 family and provides a 256 bit security level for collision resistance. The security of the hash function is mathematically approved.\cite{hash-nist}
+
diff --git a/doc/thesis/thesis.pdf b/doc/thesis/thesis.pdf
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