Implement base64url decode using OpenSSL

Author: Rudy VILLENEUVE

Makefile

@@ -7,7 +7,7 @@ CFLAGS	+= -I $(OPENSSL) -g -std=gnu99 -O3
 LDFLAGS	+= $(OPENSSL_LIB) -lcrypto -lpthread
 
 NAME	= jwtcrack
-SRCS	= main.c base64.c
+SRCS	= main.c base64url.c
 OBJS	= $(SRCS:.c=.o)
 
 all: $(NAME)

base64.c

@@ -0,0 +1,55 @@
+#include <stdlib.h>
+#include <string.h>
+#include <openssl/evp.h>
+
+// Convert base64url to base64
+// Fix b64 alignement
+// Replace '-' by '+' and '_' by '/'
+static unsigned char *base64url_to_base64(const unsigned char *base64) {
+	size_t base64len = strlen(base64);
+	// \0 + possible padding
+	unsigned char *nbase64 = malloc(base64len + 3);
+
+	memset(nbase64, 0, base64len + 3);
+	strcat(nbase64, base64);
+
+	// Fix b64 alignement
+	while (base64len % 4 != 0) {
+		nbase64[base64len++] = '=';
+	}
+	for (int i = 0; i < base64len; ++i) {
+		if (nbase64[i] == '-')
+			nbase64[i] = '+';
+		if (nbase64[i] == '_')
+			nbase64[i] = '/';
+	}
+	return nbase64;
+}
+
+int base64url_decode(const unsigned char *in, unsigned char **out)
+{
+    size_t inlen, outlen;
+    
+	unsigned char *outbuf;
+	unsigned char *base64 = base64url_to_base64(in);
+
+	inlen = strlen(base64);
+    outlen = (inlen / 4) * 3;
+    outbuf = malloc(outlen);
+    if (outbuf == NULL) {
+        goto err;
+    }
+
+    outlen = EVP_DecodeBlock(outbuf, (unsigned char *)base64, inlen);
+    if (outlen < 0) {
+        goto err;
+    }
+
+    *out = outbuf;
+	free(base64);
+    return outlen;
+err:
+	free(base64);
+    free(outbuf);
+    return -1;
+}

base64.h

@@ -0,0 +1,14 @@
+#ifndef _BASE64_H_
+#define _BASE64_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int base64url_decode(const unsigned char *in, unsigned char **out);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif //_BASE64_H_