Engineering Notes

SYSTEMS,power system analysis, transformators, power system protection
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Atmega, atmel, pic, Stm, arm,microcontrollers.

Hacking ECDSA based Digital Signature Algorithm

Posted on by bot net
  • ECDSA is newer and is based on DSA. It has the same weaknesses as DSA, but it is generally thought to be more secure, even at smaller key sizes. It uses the NIST curves (P256).
  • RSA is well-regarded and supported everywhere. It is considered quite secure. Common key sizes go up to 4096 bits and as low as 1024. The key size is adjustable. You should choose RSA.
  • DSA is not in common use anymore, as poor randomness when generating a signature can leak the private key. In the past, it was guaranteed to work everywhere as per RFC 4251, but this is no longer the case. DSA has been standardized as being only 1024 bits (in FIPS 186-2, though FIPS 186-3 has increased that limit). OpenSSH 7.0 and newer actually disable this algorithm.
  • Ed25519, while not one you listed, is available on newer OpenSSH installations. It is similar to ECDSA but uses a superior curve, and it does not have the same weaknesses when weak RNGs are used as DSA/ECDSA. It is generally considered to be the strongest mathematically.

The video contains very nice example.

 

Reference guide for current carrying capacities for PVC twin and earth cables

Posted on by bot net

Reference guide for current carrying capacities for PVC twin and earth cables

Reference Method

Description

1/1mm2
(A)

1.5/1mm2
(A)

2.5/1.5mm2
(A)

4/1.5mm2
(A)

6/2.5mm2
(A)

10/4mm2
(A)

16/6mm2
(A)

A

Enclosed in conduit in insulated wall

11.5

14.5

20

26

32

44

57

B

Enclosed in conduit or trunking on a wall

13

16.5

23

30

38

52

69

C

Clipped direct

16

20

27

37

47

64

85

100

Above plasterboard ceiling coved by insulation not exceeding 100mm thick

13

16

21

27

34

45

57

101

Above plasterboard ceiling coved by insulation exceeding 100mm thick

10.5

13

17

22

27

36

46

102

In stud wall in with insulation with cable touching inner wall

13

16

21

27

35

47

63

103

In stud wall in with insulation with cable not touching inner wall

8

19

13.5

17.5

23.5

32

42.5

 

Ratings shown are tabulated values from BS7671 Appendix 4 for 70°C PVC cables. Where appropriate, other rating factors must be applied.

Initial Magnetic Field Distribution Around High Rectangular Bus Bars Grigore A. Cividjian 1

Posted on by coder

SERBIAN JOURNAL OF ELECTRICAL ENGINEERING
Vol. 11, No. 4 (special issue), December 2014, 523-534

 

Abstract: The one-dimensional transient electromagnetic field in and around a
system of two nonmagnetic homogenous rectangular high thin bars can be
analytically evaluated if the ratio of average initial magnetic field on the two
sides of thin bar, or of the ratio of initial magnetic fields in middle of the bar
height is known. In this paper, using appropriate conformal mappings, an exact
analytical solution for these ratios are proposed in the case of very thin bars.
Obtained values are compared with FEM results for relatively thick bars.
Keywords: Conform mapping, Initial magnetic field, Elliptic integrals.
Introduction
The problem of transient electromagnetic fields for a system of two
infinite-high and long non-magnetic bars in cases of current and voltage step
application is completely studied and brilliantly solved in [1], considering the
magnetic field on internal side of the bars constant and evenly distributed and
on the external side of the bars equal to zero.

For more Please click the document to Download : Download PDF : 1-Cividjian