1. Symmetric encrypt
openssl enc -aes-256-cbc encrypts a file with AES using one shared secret key — fast, for bulk data.
openssl enc -aes-256-cbc -in f.txt -out f.encTyporithm · medium
Symmetric vs Asymmetric
symmetric-asymmetricsecurityaesrsakeypair
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Step 1 of 8 · intro card
Learn Symmetric vs Asymmetric
Cryptography
Symmetric crypto (AES) uses one shared secret key and is fast, good for bulk data. Asymmetric crypto (RSA/ECC) uses a public/private keypair for key exchange and signatures. Real systems are hybrid: asymmetric to exchange a fast symmetric session key.
Symmetric encryption uses a single secret key for both encryption and decryption. AES (here AES-256-CBC) is the standard; it is fast and ideal for encrypting large amounts of data, but both sides must already share the key.
Asymmetric encryption uses a keypair: a public key anyone can hold and a private key kept secret. Data encrypted with the public key can only be decrypted with the private key, and signatures work the reverse way — enabling key exchange and authentication without a pre-shared secret.
Asymmetric operations are slow, so real systems are hybrid: they use RSA or ECDH to securely agree on a random symmetric session key, then encrypt the actual traffic with fast AES. This is exactly how TLS sets up a connection.
01
Symmetric (AES): one shared key, fast, for bulk data.
02
Asymmetric (RSA/ECC): public/private keypair for exchange and signatures.
03
Hybrid: asymmetric exchanges a symmetric session key.
openssl enc -aes-256-cbc -in f.txt -out f.enc
openssl genrsa -out private.pem 2048
openssl rsa -in private.pem -pubout -out public.pem
openssl pkeyutl -encrypt -pubin -inkey public.pemRead the implementation
Connect each part of the code to the concept before you type.
2. Generate keypair
genrsa creates a 2048-bit RSA private key; the matching public key is derived from it.
openssl genrsa -out private.pem 20483. Extract public key
-pubout writes only the public half, which you can share freely while the private key stays secret.
openssl rsa -in private.pem -pubout -out public.pem4. Encrypt with public key
pkeyutl -encrypt -pubin encrypts with the public key so only the private-key holder can decrypt.
openssl pkeyutl -encrypt -pubin -inkey public.pemA complete learning loop
01
Understand
Read the concept map and follow the code breakdown.
02
Reconstruct
Type the implementation, repair mistakes and work through every recall exercise.
03
Verify
Use the final check without hints; revisit weak concepts in short practice sessions.