From 0f794020c7e7c59c77af58f9bdf5641d0f592966 Mon Sep 17 00:00:00 2001
From: Gentoo <installgentoo@endianness.com>
Date: Sun, 27 Sep 2020 11:08:16 +1000
Subject: initial commit

---
 Makefile | 14 ++++++++++++++
 main.c   | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)
 create mode 100644 Makefile
 create mode 100644 main.c

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..5abdc0c
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,14 @@
+CC=gcc
+CFLAGS=-O3 -march=native -pipe
+
+OBJ = main.o
+
+%.o: %.c $(DEPS)
+	$(CC) -c -o $@ $< $(CFLAGS)
+
+decode: $(OBJ)
+	$(CC) -o $@ $^ $(CFLAGS)
+
+clean:
+	rm $(OBJ)
+	rm decode
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..c93f4f1
--- /dev/null
+++ b/main.c
@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+void decodeEmail(char encoded[])
+	{
+	int len = strlen(encoded);
+
+	char temp[3];
+	char email[len/2];//the encoded string/2 gives the length of the result email+1
+
+	memcpy(temp, encoded, 2);
+	temp[2] = '\0';
+
+	char xorKey = strtol(temp, NULL, 16);//the value of the xorKey is the first two bytes in hex, encoded in UTF-8
+
+	int j = 0;
+	for (int i = 2; i < len; i += 2, ++j)//decode the rest of the two bytes
+		{
+		memcpy(temp, encoded+i,2);
+		temp[2] = '\0';
+
+		email[j] = strtol(temp, NULL, 16) ^ xorKey;//xor two bytes with the xorkey to get a UTF-8 character
+		}
+	email[j] = '\0';//terminate the string
+
+	printf("Decoded email: %s\n", email);
+	}
+
+
+
+int main(int argc, char *argv[])
+	{
+	if (!argv[1])
+		{
+		char input[512+1];//as the maximun length of an email should be 255 chars, we allocate 255*2+2 chars for the longest valid input (+1 for the newline)
+		fprintf(stderr,"Input email to decode (string within data-cfemail=\"\"): ");
+
+		ssize_t length = read(0, input, 512);
+		if (length < 5){fprintf(stderr,"Invalid input.\n"); exit(1);}
+
+		input[length-1] = '\0';//overwrite newline with null char
+
+		decodeEmail(input);
+		}
+	else
+		{
+		if (strlen(argv[1]) < 4 || strlen(argv[1]) > 512){fprintf(stderr,"Invalid input.\n"); exit(1);}
+		decodeEmail(argv[1]);
+		}
+
+	//test string: e4908d9497a4908b9696818a90829681858fca878b89
+	}
+
-- 
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