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68 lines
2.1 KiB
ReStructuredText
68 lines
2.1 KiB
ReStructuredText
Symmetric Encryption vs Public Key Encryption
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#############################################
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:date: 2012-02-13 17:25
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:author: Russell Ballestrini
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:tags: Security, Python
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:slug: symmetric-encryption-vs-public-key-encryption
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:status: published
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**How many keys are involved for symmetric key encryption? How about
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public key encryption?**
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Suppose you have N people who want to communicate with each other using
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symmetric keys. All communication between any two people, i and j, is
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visible to group N. Only person i and person j can decrypt each others
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messages.
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**How many keys would Symmetric Encryption require to protect group N?**
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I solved this with the following python function:
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::
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def count_symmetric_keys( N=2 ):
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"""Provide the number of entities in group N.
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return the number of symmetric keys needed for this group"""
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keys = 0
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for i in range( 0, N ): keys += i
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return keys
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A reader suggested the following optimized formula:
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::
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def calc_symmetric_keys( N=2 ):
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"""Provide the number of entities in group N.
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return the number of symmetric keys needed for this group"""
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return N*(N-1)/2
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.. raw:: html
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</p>
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If group N had 10 members, it would need to generate and maintain 45
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Symmetric Keys.
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If group N had 50 members, it would need to generate and maintain 1225
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Symmetric Keys.
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Symmetric keys are also susceptible to man-in-the-middle attacks. This
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attack occurs when an entity poses as a trusted entity. Let i and j be
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trusted entities. Let k be an untrusted attacker. If k determined the
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Symmetric key it could send or receive messages posing as i or j.
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**How many keys would Public-key Encryption require to protect group
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N?**
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Public Key Encryption requires 2n keys or two keys per person in group
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N. Public key encryption also does not require 'pre sharing' the secret
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key before communication may start. Each member would need 1 public key
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and 1 private key.
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If group N had 10 members, it would need to generate and maintain 20
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Public/Private Keys.
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If group N had 50 members, it would need to generate and maintain 100
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Public/Private Keys.
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.. contents::
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