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Mariano Guerra's Log

This is my blog, more about me at marianoguerra.github.io

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Public/Private Key Encryption, Sign and Verification in Erlang

You want to encrypt/decrypt some content?

You want to generate a signature and let others verify it?

At least that's what I wanted to do, so here it is.

First generate keys if you don't have some available:

openssl genrsa -out private.pem 2048
openssl rsa -in private.pem -out public.pem -outform PEM -pubout

Load the raw keys:

{ok, RawSKey} = file:read_file("private.pem").
{ok, RawPKey} = file:read_file("public.pem").

[EncSKey] = public_key:pem_decode(RawSKey).
SKey = public_key:pem_entry_decode(EncSKey).

[EncPKey] = public_key:pem_decode(RawPKey).
PKey = public_key:pem_entry_decode(EncPKey).

Let's encrypt a message with the private key and decrypt with the public key:

Msg = <<"hello crypto world">>.
CMsg = public_key:encrypt_private(Msg, SKey).
Msg = public_key:decrypt_public(CMsg, PKey).

We can do it the other way, encrypt with the public key and decrypt with the private key:

CPMsg = public_key:encrypt_public(Msg, PKey).
Msg = public_key:decrypt_private(CPMsg, SKey).

Let's generate a signature for the message that others can verify with our public key:

Signature = public_key:sign(Msg, sha256, SKey).
public_key:verify(Msg, sha256, Signature, PKey).

% let's see if it works with another message
public_key:verify(<<"not the original message">>, sha256, Signature, PKey).