Crypto libraries
OpenSSL (cont.)
Milan Brož
xbroz@fi.muni.cz
PV181, FI MUNI, Brno
OpenSSL – www.openssl.org
 opensource cryptography toolkit
 OpenSSL3 ~ released 2021, many API improvements
 Apache-style license
 hash, symmetric/asymmetric encryption, PKI, CA, ...
 ASN.1, PKCS-5,7,8,12, X509, OCSP, PEM, SSL, TLS
 command line tool
 C/C++ library bindings (+many other library wrappers)
 on Linux compile with -lcrypto –lssl
 #include <openssl/...>
Today’s goals
 Symmetric encryption
 Encryption modes
ECB, CBC, CTR, XTS
IV – initialization vector, tweak
 OpenSSL I/O abstraction (BIO)
 Demonstration of failures/mistakes
ECB use,
CBC mangled IV, CBC mangled ciphertext,
XTS patterns
CTR stream reuse
Example 4:
Symmetric encryption
OpenSSL (3.x)
Encryption with EVP interface. Cipher mode is for example ”AES-256-CBC”.
cipher = EVP_CIPHER_fetch(cipher_mode, ...)
EVP_CIPHER_CTX_new()
EVP_EncryptInit_ex2(context, cipher, key, iv, PARAMS)
EVP_EncryptUpdate(context, ciphertext, &clen, plaintext, plen)
EVP_EncryptFinal_ex(context, ciphertext + clen, &len)
EVP_CIPHER_CTX_free(context)
EVP_CIPHER_free(cipher)
See 4_encryption_openssl3 directory.
Example 7:
OpenSSL BIO (I/O abstraction)
Source/sink BIOs:
BIO_s_mem() - memory I/O
BIO_s_file() - file I/O
BIO_s_fd() - file descriptor IO
BIO_s_socket() - sockets
BIO_s_accept()
BIO_s_connect()
BIO_s_null() - discard (like /dev/null)
Filters
BIO_f_base64() - Base64 encoding
BIO_f_buffer() - buffering I/O
BIO_f_cipher() - encryption/decryption
BIO_f_md() - message digest
BIO_f_ssl() - SSL support for BIO
Example 7: the same encryption as in Example 4 using BIO interface.
See 7_bio_openssl directory.
Symmetric Encryption
common mistakes or failures
See 6_encryption_fails_openssl example in git.
Comment out various sections a play with demos.
Note there is no data integrity protection in these modes.
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Example 1: ECB patterns
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Example 2: CBC IV bit flips
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Example 3: CBC bit flips in a consecutive block
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Example 4: XTS constant IV block patterns
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Example 5: CTR stream reuse
Symmetric encryption:
ciphertext
ECB mode
…should be never used
Wrong use demo: ciphertext patterns, block relocation.
See 6_encryption_fails_openssl directory.
picture: Wikipedia
CBC mode
Wrong use demo: first block bit flips (IV) and consecutive block change.
See 6_encryption_fails_openssl directory.
picture: Wikipedia
XTS mode
storage (file, disk) encryption
Wrong use demo: block patterns with constant IV.
See 6_encryption_fails_openssl directory.
picture: Wikipedia
Symmetric encryption fails:
patterns in ciphertext
CTR (counter) mode
Wrong use demo: re-use key from known ciphertext/plaintext pair.
See 6_encryption_fails_openssl directory.
picture: Wikipedia