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What is SSHA generated by slappaasswd in OpenLDAP

· One min read

What is the slappaasswd command?​

The slappaasswd command is a command for generating passwords for OpenLDAP, which uses SSHA by default to hash the password.

Authentication mechanism​

In SSHA, the last 4 bytes of the generated hash are the salt. Authentication is performed by generating a hash from the input password and the stored salt, and checking if it matches the stored hash.

The following program, when given a valid password (e.g., admin), will produce the same original hash and generated hash.

require 'base64'
require 'digest'

pass = 'admin'
ssha = '{SSHA}23AUBfRZytVFNpe7onuFhyCSJOHRzCWh'
ssha =~ /{.+}(.+)/
salt256s = Base64.decode64(Regexp.last_match(1)).unpack('C*'[-4..-1])

salt = salt256s.pack('C*')
b_ssha = Digest::SHA1.digest(pass + salt)
Base64.strict_encode64(
 (b_ssha.unpack('C*') + salt256s).pack('C*')
)

[EOL]

Migration of Blog Environment

· One min read

We have migrated the blog environment from Jekyll to Doctusaurus. We plan to migrate frequently accessed articles from Jekyll as well.

Detecting extreme values ​​in Python

· 2 min read

Detecting extrema in a signal.​

Generating a spurious signal as an example.​

  • 3 [Hz] signal + 0.01 [Hz] signal + noise
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd
from scipy import signal

tmp

Examining the properties of the signal.​

def acorr(df: pd.DataFrame, ra: int = 3, fs=100):
   x = np.correlate(df.Data.values, df.Data.values, mode='full')
   t = (np.arange(len(x)) - len(x) / 2 + 0.5) / fs
   x /= x.max()
   fig, ax = plt.subplots()
   ax.set_xlim(-ra, ra)
   ax.set_ylim(0, 1)
   ax.plot(t, x)
   ax.set_title('Autocorrelation')
   ax.grid(axis='x')
   ax.set_xticks(np.linspace(-ra, ra, 2 * ra + 1))
   plt.show()

acorr(df)

The main signal is 1/3 [Hz]. Therefore, a low-pass filter with a cutoff of 1/3 [Hz] is applied.

tmp

Applying a low-pass filter and detecting extrema.

If the extrema are not correctly detected even after applying a low-pass filter at 1/3 [Hz], the frequency is lowered.

tmp

fs = 10
lpf = 0.1
b, a = signal.butter(5, lpf / fs * 2, 'low')
df['Filter'] = signal.filtfilt(b, a, df.Data.values)
max_idx = signal.argrelextrema(df['Filter'].values, np.greater)[0]
min_idx = signal.argrelextrema(df['Filter'].values, np.less)[0]

df['max_index'] = False
df.iloc[max_idx[0], 2] = True
df['min_index'] = False
df.iloc[min_idx[0], 3] = True

fig, ax = plt.subplots()
df.plot(ax=ax)
ax.set_xlim(['00:00:00', '00:00:30'])
ax.scatter(
   df.loc[df['max_index'], ['Filter']].index, 
   df.loc[df['max_index'], ['Filter']], 
   color='tab:orange', 
   zorder=3)
ax.scatter(
   df.loc[df['min_index'], ['Filter']].index, 
   df.loc[df['min_index'], ['Filter']], 
   color='tab:green', 
   zorder=3)
plt.show()

Handling 2D arrays in C

· One min read

It is convenient to manage memory where numbers are stored by summarizing the number of rows, number of columns, and the memory itself in a structure.

#include <stdio.h>
#include <stdlib.h>

typedef struct {
 float *data;
 int col_size;
 int row_size;
} Mat;

void MatInit(Mat *mat, int row_size, int col_size) {
 mat->row_size = row_size;
 mat->col_size = col_size;
 mat->data = (float *)calloc(row_size * col_size, sizeof(float));
}

float *MatAt(Mat *mat, int i, int j) {
 return mat->data + i * mat->col_size + j;
}

void MatFree(Mat *mat) { free(mat->data); }

int main(void) {
 Mat mat;
 MatInit(&mat, 30, 5); // Initialize a matrix with 30 rows and 5 columns
 *MatAt(&mat, 0, 0) = 50; // Assign 50 to row 0, column 0
 printf("%f\n", *MatAt(&mat, 0, 0)); // Print the value at row 0, column 0

 MatFree(&mat);

 return 0;
}
Tags:

Implementation of NMF (HALS)

· One min read
import numpy as np

X = np.array([[1, 1], [2, 1], [3, 1.2], [4, 1], [5, 0.8], [6, 1]])

n_components, n_samples, n_features, = (2,) + X.shape
W = np.random.uniform(size = (n_samples, n_components))
H = np.random.uniform(size = (n_components, n_features))

eps = 1e-4

# NMF
for i in range(100):
   # update B
   A = X.T.dot(W)
   B = W.T.dot(W)
   for j in range(n_components):
       tmp = H[j, :] + A[:, j] - H.T.dot(B[:, j])
       H[j, :] = np.maximum(tmp, eps)

   # update A
   C = X.dot(H.T)
   D = H.dot(H.T)
   for j in range(n_components):
       tmp = W[:, j] * D[j, j] + C[:, j] - W.dot(D[:, j])
       W[:, j] = np.maximum(tmp, eps)
       norm = np.linalg.norm(W[:, j])
       if norm > 0:
           W[:, j] /= norm

print(W)
print(H)
print(W.dot(H))

Setting up a DNS server in WSL2

· One min read

Disabling automatic generation of /etc/resolv.conf​

Edit /etc/wsl.conf as follows:

[network]
generateResolvConf = false

Creating /etc/resolv.conf​

For example, if the DNS server is 1.1.1.1, edit /etc/resolv.conf as follows:

nameserver 1.1.1.1

Preventing Deletion​

/etc/resolv.conf is deleted when WSL2 is restarted. To prevent this:

sudo chattr +i /etc/resolv.conf

Reference

When nokogiri cannot be installed under brew

· One min read

The following two errors occurred:

zlib is missing; necessary for building libxml2
xslt is missing. Please locate mkmf.log to investigate how it is failing.

Solution

  • Install libxslt and libxml2
  • Specify the path of libxml2 installed by brew
brew install libxslt libxml2
bundle config build.nokogiri --use-system-libraries --with-xml2-include=$(brew --prefix libxml2)/include/libxml2

Reference sites

Windows OpenSSH Permission denied issue

· One min read
  • Password login is possible (although disabled in the settings)
  • Permission denied occurs when using public key authentication

When connecting to localhost:22, the following error occurs:

hikari@localhost: Permission denied (publickey,keyboard-interactive).

image

Cause

It appears that the Administrators group, i.e., "administrator users", is referencing the public key in C:\ProgramData\ssh\administrators_authorized_keys for authentication by default.

Change this to $env:userprofile\.ssh\authorized_keys.

Solution

Open C:\ProgramData\ssh\sshd_config with administrator privileges and comment out the following two lines:

image

- Match Group administrators
-       AuthorizedKeysFile __PROGRAMDATA__/ssh/administrators_authorized_keys
+ #Match Group administrators
+ #      AuthorizedKeysFile __PROGRAMDATA__/ssh/administrators_authorized_keys

After saving, restart the service.

Restart-Service sshd

Installing Powermline on Termux

· One min read
pkg install golang

Powermline Installation

This is almost the same as the Powermline installation method

go get -u github.com/justjanne/powermline-go

Setting in .profile

Open ~/ .profile and add the following:

GOPATH=$HOME/go
function _update_ps1() {
   PS1="$( $GOPATH/bin/powermline-go -newline -error $? )"
}
if [ "$TERM" != "linux" ] && [ -f "$GOPATH/bin/powermline-go" ]; then
   PROMPT_COMMAND="_update_ps1; $PROMPT_COMMAND"
fi

Font Setup

For example, install yuru7/PlemolJP.

wget https://github.com/yuru7/PlemolJP/releases/download/v0.4.0/PlemolJP_NF_v0.4.0.zip
unzip PlemolJP_NF_v0.4.0.zip
cp PlemolJP_NF_v0.4.0/PlemolJP35Console_NF/PlemolJP35ConsoleNF-Medium.ttf $HOME/.term
ux/font.ttf
rm PlemolJP_NF_v0.4.0 -rf
rm PlemolJP_NF_v0.4.0.zip