decrypt_meta_data.c

#include <string.h>
#include <stdio.h>
#include <assert.h>

#include <openssl/evp.h>
#include <openssl/bio.h>
#include <openssl/pem.h>
#include <openssl/engine.h>

// Taken from https://gist.github.com/barrysteyn/7308212
size_t calcDecodeLength(const char* b64input) { //Calculates the length of a decoded string
	size_t len = strlen(b64input),
		padding = 0;

	if (b64input[len-1] == '=' && b64input[len-2] == '=') //last two chars are =
		padding = 2;
	else if (b64input[len-1] == '=') //last char is =
		padding = 1;

	return (len*3)/4 - padding;
}

// Taken from https://gist.github.com/barrysteyn/7308212
int Base64Decode(char* b64message, unsigned char** buffer, size_t* length) { //Decodes a base64 encoded string
	BIO *bio, *b64;

	int decodeLen = calcDecodeLength(b64message);
	*buffer = (unsigned char*)malloc(decodeLen + 1);
	(*buffer)[decodeLen] = '\0';

	bio = BIO_new_mem_buf(b64message, -1);
	b64 = BIO_new(BIO_f_base64());
	bio = BIO_push(b64, bio);

	BIO_set_flags(bio, BIO_FLAGS_BASE64_NO_NL); //Do not use newlines to flush buffer
	*length = BIO_read(bio, *buffer, strlen(b64message));
	assert(*length == decodeLen); //length should equal decodeLen, else something went horribly wrong
	BIO_free_all(bio);

	return (0); //success
}

// Taken from https://gist.github.com/barrysteyn/7308212
int Base64Encode(const unsigned char* buffer, size_t length, char** b64text) {
	BIO* bio;
    BIO* b64;
	BUF_MEM* bufferPtr;

	b64 = BIO_new(BIO_f_base64());
	bio = BIO_new(BIO_s_mem());
	bio = BIO_push(b64, bio);

	BIO_set_flags(bio, BIO_FLAGS_BASE64_NO_NL);
	BIO_write(bio, buffer, length);
	BIO_flush(bio);
	BIO_get_mem_ptr(bio, &bufferPtr);
	BIO_set_close(bio, BIO_NOCLOSE);
	BIO_free_all(bio);

	//*b64text=(*bufferPtr).data;

	return (0); //success
}

int main(int argc, char **argv) {

    char private[] = "-----BEGIN RSA PRIVATE KEY-----\n"
"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\n"
"-----END RSA PRIVATE KEY-----";


    char md[] = "M20PkGB5sm95+xPVghQWkQ==";
    char me[] = "XPUVMfWoncNybAiLFcYpFgL6cnKH4rt80nc1NEsZfp2FleWkYIzkNN7GD01k0qVdnFZGKreaLceZ+QnPPLMsbuhF50hcMPQN2wRYTQMfsxX1vk/C6RShGX18/xp19Fg8aVTMCORIyCXpXHHwdboOaz1gdJYlDydhXD37xKNxdiGBbR/7d1E25E59Hnx331jO8aeaje7YW5F/g0GzEWNXvWSkXKWCuhtepgX/WwBQspyDcarpvKkALb7KdzGxq2OcpWGEcjoDsAU3IghmbIDYxm+f5wk/D/kBTr/0UIY+wlV+h8peBEVbqTk/1hmzolU25jDEvvIVSxRQ/cs27cv1gQ==";

    BIO *bio = BIO_new(BIO_s_mem());
    BIO_write(bio, private, strlen(private));

    EVP_PKEY *key = PEM_read_bio_PrivateKey(bio, NULL, NULL, NULL);

    if (key == NULL) {
        printf("COULD NOT PARSE KEY\n");
        return -1;
    }

    unsigned char *me2 = NULL;
    size_t me2_l;
    Base64Decode(me, &me2, &me2_l);

    ENGINE *e = ENGINE_get_default_RSA();

    EVP_PKEY_CTX *ctx = EVP_PKEY_CTX_new(key,e);

    if (ctx == NULL) {
        printf("COULD NOT INIT CTX\n");
        return -2;
    }

    int err = EVP_PKEY_decrypt_init(ctx);
    if (err != 1) {
        printf("INIT ERROR\n");
        return -3;
    }
    
    err = EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_OAEP_PADDING);
    if (err <= 0) {
        printf("RSA PADDING SET\n");
        return -5;
    }

    err = EVP_PKEY_CTX_set_rsa_oaep_md(ctx, EVP_sha256());
    if (err <= 0) {
        printf("RSA OEAP MD\n");
        return -6;
    }

    err = EVP_PKEY_CTX_set_rsa_mgf1_md(ctx, EVP_sha256());
    if (err <= 0) {
        printf("RSA MGF1\n");
        return -7;
    }

    unsigned char *out = NULL;
    size_t outlen = 0;

    err = EVP_PKEY_decrypt(ctx, NULL, &outlen, me2, me2_l);
    if (err <= 0) {
        printf("DECRYPT ERROR\n");
        return -5;
    }

    printf("Len = %d\n", outlen);
    
    out = (unsigned char *)calloc(sizeof(char), outlen);

    err = EVP_PKEY_decrypt(ctx, out, &outlen, me2, me2_l);
    if (err <= 0) {
        printf("DECRYPT ERROR\n");
        return -5;
    }

    printf("1: %s\n", out);
    printf("2: %s\n", md);

    unsigned char *mk = NULL;
    size_t mk_l;
    Base64Decode(out, &mk, &mk_l);

    printf("3: %s\n", mk);


    return 0;
}