One time pad - Revision history

Pbug at 13:14, 16 December 2010

2010-12-16T13:14:17Z

← Older revision		Revision as of 06:14, 16 December 2010
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	A one time pad takes plaintext and a pad (random garble) and [[XOR]]s it together. Another person who has the same pad can then decipher this.		A one time pad takes plaintext and a pad (random garble) and [[XOR]]s it together. Another person who has the same pad can then decipher this. A pad must never be re-used and must be discarded after deciphering.

	Here is an example in C how a one time pad program might look like:		Here is an example in C how a one time pad program might look like:

Pbug: an example of using an otp

2010-12-16T13:13:15Z

an example of using an otp

← Older revision		Revision as of 06:13, 16 December 2010
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	00000080 69 6e 65 20 50 4c 41 49 4e 20 30 0a 23 64 65 66 \|ine PLAIN 0.#def\|		00000080 69 6e 65 20 50 4c 41 49 4e 20 30 0a 23 64 65 66 \|ine PLAIN 0.#def\|
	00000090 69 6e 65 20 50 41 44 20 31 0a 0a 0a 69 6e 74 0a \|ine PAD 1...int.\|		00000090 69 6e 65 20 50 41 44 20 31 0a 0a 0a 69 6e 74 0a \|ine PAD 1...int.\|


			A One Time Pad can be used by aircraft carriers who launch airplanes. The pad is made just seconds before launch in a secure part of the ship (data center) and uploaded through an umbilical cord to the airplane. Depending on how much of the pad is stored will securely encrypt communications between this carrier and the airplane. If the carrier sinks, the airplane has to switch to other secure communications to talk to other friendlies.

Pbug: example of an otp

2010-12-16T13:07:01Z

example of an otp

← Older revision		Revision as of 06:07, 16 December 2010
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	Here is an example in C how a one time pad program might look like:		Here is an example in C how a one time pad program might look like:
			#include <sys/types.h>
			#include <sys/stat.h>
			#include <fcntl.h>
			#include <unistd.h>
			#include <stdio.h>
			#include <stdlib.h>

			#define PLAIN 0
			#define PAD 1

			int
			main(int argc, char *argv[])
			{
			struct stat sb[2];
			int fd[2];
			u_char c, p;

			if (argc != 3) {
			fprintf(stderr, "usage: otp [plaintext] [pad]\n");
			exit(1);
			}

			fd[PLAIN] = open(argv[1], O_RDONLY, 0);
			if (fd[PLAIN] < 0) {
			perror("open [PLAIN]");
			exit(1);
			}
			if (fstat(fd[PLAIN], &sb[PLAIN]) < 0) {
			perror("fstat [PLAIN]");
			exit(1);
			}
			fd[PAD] = open(argv[2], O_RDONLY, 0);
			if (fd[PAD] < 0) {
			perror("open [PAD]");
			exit(1);
			}
			if (fstat(fd[PAD], &sb[PAD]) < 0) {
			perror("fstat [PAD]");
			exit(1);
			}
			if (sb[PAD].st_size < sb[PLAIN].st_size) {
			fprintf(stderr, "pad must be larger or equal in size to plaintext\n");
			exit(1);
			}
			while (read(fd[PLAIN], &c, sizeof(c)) > 0) {
			if (read(fd[PAD], &p, sizeof(p)) < 0) {
			perror("read [PAD]");
			exit(1);
			}
			c ^= p;
			write(STDOUT_FILENO, &c, 1);
			}

			return 0;
			}


			And here is how it would be used:

			atlas$ dd if=/dev/random of=pad bs=512 count=2
			2+0 records in
			2+0 records out
			1024 bytes transferred in 0.000057 secs (17970574 bytes/sec)
			atlas$ ./otp otp.c pad \| tee ciphertext \| hexdump -C \| head
			00000000 47 41 5c ff 5a 58 8a bc dd 69 90 88 be 3c 56 12 \|GA\.ZX...i...<V.\|
			00000010 27 bd 65 18 37 1a c2 86 c8 d5 c6 31 ef ad 4d c2 \|'.e.7......1..M.\|
			00000020 30 91 68 c0 ab 1a 74 77 5a 90 66 7f 4f 11 ea 05 \|0.h...twZ.f.O...\|
			00000030 d4 99 24 d9 15 86 59 64 e0 6f 7c 9d 4a 36 ee 2a \|..$...Yd.o\|.J6.*\|
			00000040 04 52 38 3e 23 b1 73 e8 53 57 3c 14 11 5e ba df \|.R8>#.s.SW<..^..\|
			00000050 3e 3b 44 2c c1 bc 42 10 1a 6f 04 90 30 e7 9f 26 \|>;D,..B..o..0..&\|
			00000060 0a 12 47 e7 70 3e 1d 3e 9c 77 3c 9c 9f 50 31 49 \|..G.p>.>.w<..P1I\|
			00000070 de d3 cf ed 51 8d 78 04 a0 70 8d d7 cc bd 2a f5 \|....Q.x..p....*.\|
			00000080 7b 72 66 82 83 76 6b 71 6e f6 6a ba 6f 11 1c 57 \|{rf..vkqn.j.o..W\|
			00000090 c6 41 25 ce bb 3f 80 9d 3e 82 fc bb 9f 4b d9 b7 \|.A%..?..>....K..\|
			atlas$ ./otp ciphertext pad \| hexdump -C \| head
			00000000 23 69 6e 63 6c 75 64 65 20 3c 73 79 73 2f 74 79 \|#include <sys/ty\|
			00000010 70 65 73 2e 68 3e 0a 23 69 6e 63 6c 75 64 65 20 \|pes.h>.#include \|
			00000020 3c 73 79 73 2f 73 74 61 74 2e 68 3e 0a 23 69 6e \|<sys/stat.h>.#in\|
			00000030 63 6c 75 64 65 20 3c 66 63 6e 74 6c 2e 68 3e 0a \|clude <fcntl.h>.\|
			00000040 23 69 6e 63 6c 75 64 65 20 3c 75 6e 69 73 74 64 \|#include <unistd\|
			00000050 2e 68 3e 0a 23 69 6e 63 6c 75 64 65 20 3c 73 74 \|.h>.#include <st\|
			00000060 64 69 6f 2e 68 3e 0a 23 69 6e 63 6c 75 64 65 20 \|dio.h>.#include \|
			00000070 3c 73 74 64 6c 69 62 2e 68 3e 0a 0a 23 64 65 66 \|<stdlib.h>..#def\|
			00000080 69 6e 65 20 50 4c 41 49 4e 20 30 0a 23 64 65 66 \|ine PLAIN 0.#def\|
			00000090 69 6e 65 20 50 41 44 20 31 0a 0a 0a 69 6e 74 0a \|ine PAD 1...int.\|

Pbug: Created page with "A one time pad takes plaintext and a pad (random garble) and XORs it together. Another person who has the same pad can then decipher this. Here is an example in C how a one..."

2010-12-16T12:47:37Z

Created page with "A one time pad takes plaintext and a pad (random garble) and XORs it together. Another person who has the same pad can then decipher this. Here is an example in C how a one..."

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A one time pad takes plaintext and a pad (random garble) and [[XOR]]s it together. Another person who has the same pad can then decipher this.

Here is an example in C how a one time pad program might look like: