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+++ b/utils/README.md
@@ -1,15 +1,72 @@
-# File encryption utilities
+# Utilities
 
-Here are a couple of useful file encryption utilities built on top of the library.
-Each of the utilities accepts `--help` flag, which can be used to examine utility's usage info.
+Here are a couple of useful utilities built on top of the library.
+Each of the utilities accepts the `--help` flag, which can be used to examine utility's usage info.
 
 The included utilities are:
 
+* [block encryption](#block-encryption) utilities,
 * [file encryption](#file-encryption) utilities,
 * and [bitmap encryption](#bitmap-encryption) utilities.
 
+## Block encryption
+
 On older CPUs, you can run the utilities [using Intel SDE](https://github.com/egor-tensin/aesni#running-on-older-cpus).
 
+### aes_encrypt_block.exe
+
+Encrypts 16-byte blocks using AES-128/192/256 in the specified mode of operation.
+
+#### Usage examples
+
+For example, to encrypt
+
+* the plaintext block `0x00112233445566778899aabbccddeeff`
+* using AES-128 in ECB mode
+* with key `0x000102030405060708090a0b0c0d0e0f`,
+
+run:
+
+    aes_encrypt_block.exe -a aes128 -m ecb 000102030405060708090a0b0c0d0e0f 00112233445566778899aabbccddeeff
+
+To encrypt
+
+* the plaintext block `0x00112233445566778899aabbccddeeff`
+* using AES-192 in OFB mode
+* with initialization vector `0x22222222222222222222222222222222`
+* and key `0x000102030405060708090a0b0c0d0e0f101112131415161718`,
+
+run:
+
+    aes_encrypt_block.exe -a aes192 -m ofb 000102030405060708090a0b0c0d0e0f101112131415161718 22222222222222222222222222222222 00112233445566778899aabbccddeeff
+
+### aes_decrypt_block.exe
+
+Decrypts 16-byte blocks using AES-128/192/256 in the specified mode of operation.
+
+#### Usage examples
+
+For example, to decrypt
+
+* the ciphertext block `0x69c4e0d86a7b0430d8cdb78070b4c55a`
+* using AES-128 in ECB mode
+* with key `0x000102030405060708090a0b0c0d0e0f`,
+
+run:
+
+    aes_decrypt_block.exe -a aes128 -m ecb 000102030405060708090a0b0c0d0e0f 69c4e0d86a7b0430d8cdb78070b4c55a
+
+To decrypt
+
+* the ciphertext block `0x762a5ab50929189cefdb99434790aad8`
+* using AES-192 in OFB mode
+* with initialization vector `0x22222222222222222222222222222222`
+* and key `0x000102030405060708090a0b0c0d0e0f101112131415161718`,
+
+run:
+
+    aes_decrypt_block.exe -a aes192 -m ofb 000102030405060708090a0b0c0d0e0f101112131415161718 22222222222222222222222222222222 bda298884f5c3a9eb7068aa7063a3b75
+
 ## File encryption
 
 ### aes_encrypt_file.exe