Linux Kernel Crypto API Examples

Testing the crypto samples in the Linux kernel document.

Note: It seems the kernel crypto API v4.14 is different to v4.15+.

You can check the crypto support in kernel by:

cat /proc/crypto

The SHA384 and SHA512 might not be enabled by default, it has to turn on with:

$ make linux-menuconfig
  Cryptographic API —> SHA384 and SHA512 digest algorithm

Code Example For Symmetric Key Cipher Operation (v4.14)

Built and tested on Debian 9.x (4.14.0-3-amd64).

# cbc-aes-aesni

cd aes-example
make
sudo dmesg -C
sudo insmod aes-example.ko
sudo rmmod aes-example.ko
sudo dmesg

Code Example For Use of Operational State Memory With SHASH (v4.14+)

Modified to be built and tested on Debian 9.x (4.14.0-3-amd64).

# shash (SHA1)

cd shash-example
make
sudo dmesg -C
sudo insmod shash-example.ko
sudo rmmod shash-example.ko
sudo dmesg

Code Example For Symmetric Key Cipher Operation (v4.14+)

Cannot get compiled Debian 9.x (4.14.0-3-amd64).

# cbc-aes-aesni

cd aes-example
make
sudo dmesg -C
sudo insmod aes-example.ko
sudo rmmod aes-example.ko
sudo dmesg

Code Example For Random Number Generator Usage (v4.14+)

# rand

# load drbg module
sudo modprobe drbg

cd rand-example
make
sudo dmesg -C
sudo insmod rand-example.ko
sudo rmmod rand-example.ko
sudo dmesg

Output

[ 2223.280561] test rand loaded
[ 2223.280597] RNG returned no data
[ 2223.280599] get_random_numbers return 0
[ 2223.280600] 10
[ 2223.280600] 58
[ 2223.280600] 77
[ 2223.280601] 69
[ 2223.280601] 48
[ 2223.280602] 19
[ 2223.280602] ca
[ 2223.280602] 43
[ 2223.280603] 2b
[ 2223.280603] a0
[ 2223.280604] de
[ 2223.280604] fa
[ 2223.280604] 88
[ 2223.280605] 63
[ 2223.280605] a3

Reference

• Linux Kernel Cryptographic API for fun and profit
• Confessions of a security hardware driver maintainer
• A overview of Linux crypto subsystem
• Crypto headers: /usr/src/linux-headers-4.14.0-3-common/include/crypto