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One-time Pad Crypto Shield

secure communication through openness

One-time Pad Crypto Shield
With a wide variety of cryptography hardware and software commercially available, it may not be obvious why you would want to build your own system. Yet the reason is simple: you just can’t trust most of these devices and programs because in 99% of the cases you have no clue of what is going on inside!
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Download the BOM list
The BOM (Bill of Materials) is the technically exhaustive listing of parts and other hardware items used to produce the working and tested prototype of any Elektor Labs project. The BOM file contains deeper information than the Component List published for the same project in Elektor Magazine. If required the BOM gets updated directly by our lab engineers. As a reader, you can download the list here.
Want to learn more about our BOM list? Read the BOM list article for extra information.
Component list

Component List


Default: 0805, 125mW, 5%

R1,R18,R24 = 1.8kΩ

R2,R16,R17 = 10kΩ

R3,R21,R22 = 3.3kΩ

R4,R10,R11 = 680Ω

R5,R12,R14,R15 = 1kΩ

R6,R7,R23 = 4.7kΩ

R8 = 22kΩ

R9 = 7.5kΩ, 1%

R13 = 470Ω

R19 = 100kΩ

R20 = 1.5kΩ

P1 = 10kΩ trimpot

P2 = 1kΩ trimpot



Default: SMD 0805

C1,C2,C4,C5,C6,C7,C8,C9,C13,C16,C17,C18,C20 = 100nF

C3 = 100µF, 10V, Case B

C10,C12 = 1µF

C14,C15 = 33pF

C11 = 0.22F, 5.5V, supercap, 5mm pitch

C19 = 2.2µF, 16V, Case A



IC1 = HCPL-817-000E


IC3 = TCM3105NL


T1 = BC847C

T2 = TSM2302CX RFG

LED1,LED2,LED3 = green, 0805

LED4,LED5.LED6 = yellow, 0805

LED7 = red, 0805



K1 = 8-pin pinheader, 0.1" pitch

K2 = 10-pin pinheader, 0.1" pitch

K3,K5 = 6-pin pinheader, 0.1" pitch

K4 = 12-pin pinheader, 0.1" pitch

K6 = Micro SD card socket, Molex 47309 Series

K7,K8,K9,JP1 = 2-pin pinheader, 0.1" pitch

K10 = Micro USB type-B receptacle

S1,S2,S3 = tactile-feedback switch, 6x6.2mm, SMD

X1 = 4.433619MHz quartz crystal,

MOD1 = 12-pin (2x6) pinheader, 0.1" pitch

DIP socket, 16 contacts

PCB #160510-1, from Elektor Store



WIZ107SR Serial-to-Ethernet Module

Elektor Uno R4


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