Crypto libraries
OpenSSL II (cont.)
Milan Brož
xbroz@fi.muni.cz
PV181, FI MUNI, Brno
Today’s exercise
 Continue with OpenSSL on Linux
 Authenticated encryption
AEAD – Authenticated Encryption with Associated Data
GCM example
 OpenSSL3 ECC (elliptic curves) keygen
 Trivial TLS client
 Bonus: OpenSSL3 providers example
Why AEAD
integrity protection for data
Authenticated mode
GCM - Galois/Counter Mode
See 6_encryption_fails_openssl directory.
picture: Wikipedia
Authenticated Encryption
with Additional Data (AEAD):
confidentiality + integrity.
- additional auth. data (AAD)
- data (plaintext/ciphertext)
- authentication tag
Example 5: AEAD
Authenticated encryption
OpenSSL (3.x)
(Authenticated) encryption with EVP interface. Cipher mode is for example ”AES-256-GCM”.
EVP_CIPHER_fetch(NULL/*lib*/, "AES-256-GCM", NULL/*props*/)
EVP_CIPHER_CTX_new()
EVP_EncryptInit_ex2(context, EVP_cipher, key, iv, PARAMS[])
EVP_EncryptUpdate(context, ciphertext, &clen, plaintext, plen)
EVP_EncryptFinal_ex(context, ciphertext + clen, &len)
/* OSSL_CIPHER_PARAM_AEAD_TAG access */
EVP_CIPHER_CTX_get/set_params(ctx, PARAMS[]))
EVP_CIPHER_CTX_free(context)
EVP_CIPHER_free(EVP_cipher)
See 4_encryption_aead_openssl3 directory.
Example 8:
TLS connection & certificates
BIO TLS connection
- SSL_CTX_set_verify, SSL_get_peer_certificate,
SSL_get_verify_result
- BIO_new_ssl_connect, BIO_get_ssl, BIO_do_connect,
BIO_do_handshake
X509
- X509_STORE_CTX_get_current_cert, X509_print_ex_fp,
X509_NAME_get_entry, …
Connect to https://www.google.com.
Read and validate certificates.
Sent HTTP GET and receive /robots.txt through a secured connection.
See 8_tls_client_openssl directory.
Example 9: ECC keys,
sign & verify with ED25519
EC key (pair) generation
EVP_PKEY_CTX_new_from_name
EVP_PKEY_keygen_init
EVP_PKEY_CTX_set_params
EVP_PKEY_generate
// Also: EVP_EC_gen(), EVP_PKEY_Q_keygen()
Signature – there can be differences for different curves
ED25519: EVP_DigestSign/EVP_DigestVerify (one-shot)
Export of keys and attributes
EVP_PKEY_get_* functions
PEM_write_bio_PrivateKey
PEM_write_bio_PUBKEY
See 9_ecc_gen_openssl3 directory.
Bonus: OpenSSL3 providers
You can define you own library;
It is loaded and used through OpenSSL3 API
https://github.com/provider-corner
●
Toy example: Vigenere cipher (historic 16th
century cipher)
git clone https://github.com/provider-corner/vigenere
git submodule init
git submodule update
cmake .
make
●
Need to copy to ossl-modules dir or use config
$ echo ahoj | openssl enc -provider vigenere -e -vigenere -K 000102030405060708090a0b0c0d0e0f
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