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What is asymmetric encryption?
Asymmetric encryption is a method of encryption that uses two different keys: a public key and a private key. The public key is used to encrypt data and can be shared with anyone without hesitation. The private key, on the other hand, is kept secret and is used to decrypt the encrypted data. This enables secure communication, as only the person who has the private key can decrypt the encrypted information.
What is the difference between symmetric and asymmetric encryption?
The main difference lies in the number of keys used:
- Symmetric encryption: Here, the same key is used for both encryption and decryption. The problem here is the secure transmission of this key to the communication partner without it being intercepted.
- Asymmetric encryption: Two keys are used. The public key is available to everyone, the private key remains secret. This eliminates the need to send the secret key via insecure channels.
How does asymmetric encryption work?
The process works in two steps:
- The sender uses the recipient’s public key to encrypt a message. This key is public, which means that anyone can use it to encrypt data, but only the recipient can decrypt it.
- The recipient then decrypts the message using their private key. This key remains secret and can convert the encrypted data back into readable form.
A practical example: If I want to send you an e-mail, I encrypt it with your public key. Only you can read this email, as only you have the corresponding private key.
What is the advantage of asymmetric encryption?
The biggest advantage lies in the security of the key distribution. In contrast to symmetric encryption, where both parties need the same key, asymmetric encryption only requires the public key to be transmitted, which poses no risk. The private key always remains secret and secure with the recipient. This minimizes the risk of man-in-the-middle attacks and makes asymmetric methods particularly attractive for secure communication over insecure networks such as the internet.
When is asymmetric encryption used?
Asymmetric encryption is used in many security-critical applications, including:
- SSL/TLS: For securing HTTPS connections, as used by web browsers to encrypt communication between a browser and a server.
- Email encryption: Technologies such as PGP (Pretty Good Privacy) use asymmetric encryption to ensure that only the intended recipient can read the message.
- Digital signatures: To guarantee the authenticity and integrity of messages and software.
- Blockchain and cryptocurrencies: Private and public keys are used to sign transactions and secure the identity of users.
What are the weaknesses of asymmetric encryption?
Although asymmetric encryption offers many advantages, it also has some weaknesses:
- Computing effort: Compared to symmetric methods, asymmetric encryption is significantly slower. It requires much more computing power, which can lead to performance problems, especially when encrypting large amounts of data.
- Key management: The handling of keys is complex. The private key must be kept absolutely secure, as its loss or theft can have fatal consequences.
- Key length: To be considered secure, the keys must be sufficiently long (typically 2048 bits or more for RSA). Shorter keys are susceptible to brute force attacks.
What are public and private keys?
A public key is a cryptographic key that is freely published and can be used by anyone to encrypt data. This key can be distributed without hesitation, as it alone is not sufficient to decrypt encrypted messages. A private key, on the other hand, is kept secret and is only used by its owner. It is the only key that can decrypt encrypted data that has been encrypted with the corresponding public key. The security of the system depends on the private key remaining secret. If it is compromised, an attacker can decrypt all encrypted messages.
Which algorithms are used for asymmetric encryption?
There are several common algorithms for asymmetric encryption:
- RSA (Rivest-Shamir-Adleman): One of the oldest and best-known algorithms. It is based on the difficulty of factorizing large prime numbers.
- ECC (Elliptic Curve Cryptography): A modern alternative to RSA that offers the same security with shorter keys and therefore requires less computing power.
- DSA (Digital Signature Algorithm): Mainly used for digital signatures, based on discrete logarithms.
How secure is asymmetric encryption?
The security of asymmetric procedures depends on the key length and the mathematics used. As long as the algorithm used is strong (e.g. RSA with at least 2048 bits or ECC with 256 bits), the method is considered secure against known attacks. However, theoretical threats such as quantum computers could jeopardize these algorithms in the future, which is why research is already being carried out into post-quantum cryptography.
What are digital signatures and how are they related to asymmetric encryption?
A digital signature uses asymmetric encryption to guarantee the authenticity and integrity of a message. The sender creates a signature by running a hash function over the message and encrypting the hash with their private key. The recipient can verify this signature with the sender’s public key. If the verification is successful, the recipient knows that the message originates from the correct sender and has not been altered.
How is asymmetric encryption used in HTTPS/SSL?
HTTPS uses asymmetric encryption to establish a secure connection between a web browser and a server. First, the browser and the server exchange certificates and public keys in a so-called TLS handshake. A symmetric session key is then agreed, which is used for the actual encryption of the communication. Asymmetric encryption is therefore mainly used for secure key exchange, while the subsequent data transmission is secured by symmetric encryption.
What role does “key exchange” play in asymmetric encryption?
Secure key exchange is crucial to enable encrypted communication between two parties. Asymmetric encryption, as used in Diffie-Hellman key exchange or RSA-based handshakes, allows the parties to jointly negotiate a secret symmetric key via insecure channels. This key is then used for the actual data encryption, as symmetric methods work much faster than asymmetric ones.
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