stevedoria.net

A nonce is a value, N, that is used only once: N_once. Nonces or nonce values are encountered in cryptography.

The initialization vector used for AES in CBC mode are typically nonces:

C₁ = CIPH_K(P₁ ⊕ N_once)
C_j = CIPH_K(P_j ⊕ C_j-1) for 2 <= j <= n

Here, cipher block 1 is the result of the cipher block function keyed on K applied to the XOR value of plaintext block 1 and a nonce. The following cipher blocks are the result of the cipher block function keyed on K applied to the XOR value of the corresponding plaintext blocks and the previous cipher block.

There is a potential segmentation fault when executing ‘make test’ while building apr-1.7.0. The following lines are output:

...
testatomic          : -Line 413: Failed creating threads
-/bin/sh: line 2: XXXXX Segmentation fault      ./$prog -v
...
Programs failed: testall
make[1]: *** [check] Error 139
make[1]: Leaving directory `.../apr-1.7.0/test'
make: *** [check] Error 2

The segmentation fault is caused by a call to apr_thread_join() on an invalid apr_thread_t instance in test_atomics_threaded(). The problematic functions, test_atomics_threaded() and test_atomics_threaded64(), continue processing even when apr_thread_create() returns an error value.

The segmentation fault is avoided and the remaining tests are executed if either of the following is performed on …/apr-1.7.0/test/testatomic.c:

1. Comment out the following lines:

abts_run_test(suite, test_atomics_threaded, NULL);
abts_run_test(suite, test_atomics_threaded64, NULL);

2. Update NUM_THREADS with a smaller number, for example:

#define NUM_THREADS 25

A lack of memory resources is the underlying cause of this segmentation fault. Reducing the number of threads created for these tests allows testing the atomic operations as intended.

fciv.py is a Python module that I implemented to generate file integrity data in a format used by Microsoft File Checksum Integrity Verifier. My use case involves copying files from a Linux workstation to a Microsoft Windows workstation. I wanted to generate integrity data on Linux using Python 3 and verify file integrity on Microsoft Windows without installing 3rd party software.

FCIV file content is generated with the following Python snippet:

import fciv
digests = fciv.fciv_compute('mydirectory/**')
fciv.fciv_write(digests)

With the output of the generation script redirected to a file named ‘fciv.xml’, the following snippet performs verification:

import fciv
reference_digests = fciv.fciv_read('fciv.xml')
actual_digests = fciv.fciv_compute('mydirectory/**')
fciv.fciv_verify(actual_digests, reference_digests)

The verification performed by fciv.py reports mismatches between expected and actual file checksums. Files missing from and files in addition to that of the verification data are also reported.

From The TypeScript Handbook:

The easiest way to remember whether to use readonly or const is to ask whether your using it on a variable or a property. Variables use const whereas properties use readonly.