32 lines
1.5 KiB
Markdown
32 lines
1.5 KiB
Markdown
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---
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tags: [encryption]
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created: Friday, December 20, 2024
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---
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# bbdcb54f_public_key_cryptography
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_A_ wants to send a message to _B_. A wants to ensure that only _B_ can read the
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message and that it is not intercepted or altered during transmission to _B_.
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Think of _B_ as being in possession of a letterbox. The letterbox contains
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messages that only he can read. Anyone can put letters in it for _B_ to read but
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_B_ alone can read them.
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This is achieved by encyrpting the messages with two keys: a public key and a
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private key. The public key can be shared with others and anyone in possession
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of the public key can encrypt a message for _B_. Once encrypted, only _B_ can
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decrypt it using his private key. Once receiving the message, B uses his private
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secret key - that he doesn't share with anyone else - to decrypt. This is the
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equivalent to opening up the letterbox and taking out the letters.
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Another useful analogy is to think of invisible ink. Anyone can write a letter
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using the invisible ink but only the recipient has the liquid that can render it
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visible again. Anyone intercepting the message (without the liquid) will see
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nothing, equivalent to the encrypted data.
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This is asymmetric encryption because the two communicating parties do not have
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equal access to the messages exchanged. _A_ can only send messages - he can't
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decrypt them, only _B_ can. So _A_ is unequal relative to _B_. With symmetric
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encryption _A_ and _B_ would both share a single private key which they would
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each use to encrypt and decrypt their messages.
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