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* PUSH NOTE : 9. Public Key Encryption.md * PUSH NOTE : 3. Symmetric Key Encryption.md * PUSH ATTACHMENT : is-03-ecb-encryption.png * PUSH ATTACHMENT : is-03-cbc-encryption.png * PUSH ATTACHMENT : is-03-ctr-encryption.png * PUSH NOTE : 07. Public Key Cryptography.md * PUSH NOTE : 7. Key Exchange.md * PUSH NOTE : 03. Symmetric Key Cryptography (2).md * PUSH NOTE : 5. CCA-Security and Authenticated Encryption.md * PUSH NOTE : 6. Hash Functions.md * DELETE FILE : _posts/lecture-notes/internet-security/2023-10-03-key-exchange.md * DELETE FILE : _posts/lecture-notes/modern-cryptography/2023-09-18-symmetric-key-cryptography-2.md * DELETE FILE : assets/img/posts/lecture-notes/modern-cryptography/is-03-cbc-encryption.png * DELETE FILE : assets/img/posts/lecture-notes/modern-cryptography/is-03-ctr-encryption.png * DELETE FILE : assets/img/posts/lecture-notes/modern-cryptography/is-03-ecb-encryption.png
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@@ -15,7 +15,7 @@ date: 2023-10-09
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github_title: 2023-10-09-public-key-cryptography
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---
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In symmetric key cryptography, we have a problem with key sharing and management. More info in the first few paragraphs of [Key Exchange (Modern Cryptography)](../../modern-cryptography/2023-10-03-key-exchange).
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In symmetric key cryptography, we have a problem with key sharing and management. More info in the first few paragraphs of [Key Exchange (Modern Cryptography)](../modern-cryptography/2023-10-03-key-exchange.md).
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## Public Key Cryptography
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@@ -32,7 +32,7 @@ These keys are created to be used in **trapdoor one-way functions**.
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A **one-way function** is a function that is easy to compute, but hard to compute the pre-image of any output. Here are some common examples.
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- *Cryptographic hash functions*: [Hash Functions (Modern Cryptography)](../../modern-cryptography/2023-09-28-hash-functions/#collision-resistance).
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- *Cryptographic hash functions*: [Hash Functions (Modern Cryptography)](../modern-cryptography/2023-09-28-hash-functions.md#collision-resistance).
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- *Factoring a large integer*: It is easy to multiply to integers even if they're large, but factoring is very hard.
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- *Discrete logarithm problem*: It is easy to exponentiate a number, but it is hard to find the discrete logarithm.
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@@ -80,14 +80,14 @@ But a problem still remains. How does one verify that this key is indeed from th
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## Diffie-Hellman Key Exchange
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Choose a large prime $p$ and a generator $g$ of $\mathbb{Z}_p^{ * }$. The description of $g$ and $p$ will be known to the public.
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Choose a large prime $p$ and a generator $g$ of $\mathbb{Z}_p^\ast$. The description of $g$ and $p$ will be known to the public.
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> 1. Alice chooses some $x \in \mathbb{Z}_p^{ * }$ and sends $g^x \bmod p$ to Bob.
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> 2. Bob chooses some $y \in \mathbb{Z}_p^{ * }$ and sends $g^y \bmod p$ to Alice.
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> 1. Alice chooses some $x \in \mathbb{Z}_p^\ast$ and sends $g^x \bmod p$ to Bob.
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> 2. Bob chooses some $y \in \mathbb{Z}_p^\ast$ and sends $g^y \bmod p$ to Alice.
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> 3. Alice and Bob calculate $g^{xy} \bmod p$ separately.
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> 4. Eve can see $g^x \bmod p$, $g^y \bmod p$ but cannot calculate $g^{xy} \bmod p$.
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Refer to [Diffie-Hellman Key Exchange (Modern Cryptography)](../../modern-cryptography/2023-10-03-key-exchange/#diffie-hellman-key-exchange-(dhke)).
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Refer to [Diffie-Hellman Key Exchange (Modern Cryptography)](../modern-cryptography/2023-10-03-key-exchange.md#diffie-hellman-key-exchange-(dhke)).
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## Message Integrity
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