init

2024-07-20 13:13:27 +03:00
commit 624a774bb1
4 changed files with 251 additions and 0 deletions
@@ -0,0 +1,106 @@
+#include <string.h>
+#include <errno.h>
+
+#include "rensa.h"
+
+
+#define BUFSIZ 8192
+
+
+int rensa_encrypt(const char *plain, size_t len, const char *key, char zeroth_char, char *cipher) {
+	if (key == NULL) {
+		*(cipher++) = *(plain++) + zeroth_char;
+		for (int i = 1; i < len; i++, plain++, cipher++) {
+			*cipher = *plain + *(plain - 1);
+		}
+	} else {
+		*(cipher++) = *(plain++) + key[(unsigned char) zeroth_char];
+		for (int i = 1; i < len; i++, plain++, cipher++) {
+			*cipher = *plain + key[(unsigned char) *(plain - 1)];
+		}
+	}
+	return 0;
+}
+
+int rensa_decrypt(const char *cipher, size_t len, const char *key, char zeroth_char, char *plain) {
+	if (key == NULL) {
+		*(plain++) = *(cipher++) - zeroth_char;
+		for (int i = 1; i < len; i++, plain++, cipher++) {
+			*plain = *cipher - *(plain - 1);
+		}
+	} else {
+		*(plain++) = *(cipher++) - key[(unsigned char) zeroth_char];
+		for (int i = 1; i < len; i++, plain++, cipher++) {
+			*plain = *cipher - key[(unsigned char) *(plain - 1)];
+		}
+	}
+	return 0;
+}
+
+int rensa_fencrypt(FILE *input, FILE *output, FILE *key, size_t key_shift, char zeroth_char) {
+	if (input == NULL) {
+		input = stdin;
+	}
+	if (output == NULL) {
+		output = stdout;
+	}
+	int status;
+	size_t readcount;
+	char key_buffer[256];
+	if (key != NULL) {
+		if (fseek(key, key_shift, SEEK_SET) != 0) {
+			return errno;
+		}
+		readcount = fread(key_buffer, 1, 256, key);
+		for (int i = readcount; i < 256; i += readcount) {
+			rewind(key);
+			readcount = fread(key_buffer + i, 1, 256 - i, key);
+		}
+	}
+	char rbuffer[BUFSIZ], wbuffer[BUFSIZ];
+	while ((readcount = fread(rbuffer, 1, BUFSIZ, input)) != 0) {
+		status = rensa_encrypt(rbuffer, BUFSIZ, (key != NULL) ? key_buffer : NULL, zeroth_char, wbuffer);
+		if (status != 0) {
+			return status;
+		}
+		if (fwrite(wbuffer, 1, readcount, output) < readcount) {
+			return -1;
+		}
+		zeroth_char = rbuffer[BUFSIZ - 1];
+	}
+	return 0;
+}
+
+int rensa_fdecrypt(FILE *input, FILE *output, FILE *key, size_t key_shift, char zeroth_char) {
+	if (input == NULL) {
+		input = stdin;
+	}
+	if (output == NULL) {
+		output = stdout;
+	}
+	int status;
+	size_t readcount;
+	char key_buffer[256];
+	if (key != NULL) {
+		if (fseek(key, key_shift, SEEK_SET) != 0) {
+			return errno;
+		}
+		readcount = fread(key_buffer, 1, 256, key);
+		for (int i = readcount; i < 256; i += readcount) {
+			rewind(key);
+			readcount = fread(key_buffer + i, 1, 256 - i, key);
+		}
+	}
+	char rbuffer[BUFSIZ], wbuffer[BUFSIZ];
+	while ((readcount = fread(rbuffer, 1, BUFSIZ, input)) != 0) {
+		status = rensa_decrypt(rbuffer, BUFSIZ, (key != NULL) ? key_buffer : NULL, zeroth_char, wbuffer);
+		if (status != 0) {
+			return status;
+		}
+		if (fwrite(wbuffer, 1, readcount, output) < readcount) {
+			return -1;
+		}
+		zeroth_char = wbuffer[BUFSIZ - 1];
+	}
+	return 0;
+}