對openssl genrsa產生的rsa私鑰pem文件，使用普通的base64解碼會有問題，如使用https://blog.csdn.net/fengbingchun/article/details/85218653 中介紹的方法，一是有可能不能從返回的結果中直接使用strlen來獲得最終字符的大小，因為返回的結果中可能會有0x00；二是pem文件中會有換行符，每行的字節長度超過64個字節就會有換行，普通的base64解碼中不會對換行符有處理。在OpenSSL中，默認情況下，base64行長度限制為64個字符。

先介紹下使用命令行openssl base64進行編解碼：

(1).對” https://blog.csdn.net/fengbingchun”進行編解碼，執行命令及結果如下：

(2).對長串進行編解碼，如” https://blog.csdn.net/fengbingchun https://github.com//fengbingchun”，執行命令及結果如下：編碼長度超過64個字符長度，會進行換行，若不想換行，可增加使用”-A”選項

(3).對指定文件進行編解碼：如文件1.txt，先進行編碼生成2.txt，然后再對2.txt進行解碼生成3.txt，執行命令及結果如下：

下面是通過調用openssl的相關接口組合成的base64編解碼實現：由外部負責申請足夠的空間用于存放結果，最后一個參數用于指明編解碼中是否換行。

int openssl_base64_encode(const unsigned char* in, int inlen, char* out, int* outlen, bool newline)
{BIO* b64 = BIO_new(BIO_f_base64());BIO* bmem = BIO_new(BIO_s_mem());if (!b64 || !bmem) {fprintf(stderr, "fail to BIO_new\n");return -1;}b64 = BIO_push(b64, bmem);if (!newline)BIO_set_flags(b64, BIO_FLAGS_BASE64_NO_NL); // ignore newlines, write everything in one line*outlen = BIO_write(b64, in, inlen);if (*outlen <= 0 || *outlen != inlen) {fprintf(stderr, "fail to BIO_write\n");return -1;}BIO_flush(b64);BUF_MEM* buf = nullptr;BIO_get_mem_ptr(b64, &buf);*outlen = buf->length;memcpy(out, buf->data, *outlen);BIO_free_all(b64);return 0;
}int openssl_base64_decode(const char* in, int inlen, unsigned char* out, int* outlen, bool newline)
{BIO* b64 = BIO_new(BIO_f_base64());BIO* bmem = BIO_new_mem_buf(in, inlen);if (!b64 || !bmem) {fprintf(stderr, "fail to BIO_new\n");return -1;}b64 = BIO_push(b64, bmem);if (!newline)BIO_set_flags(b64, BIO_FLAGS_BASE64_NO_NL); // ignore newlines, write everything in one line*outlen = BIO_read(b64, out, inlen);if (*outlen <= 0) {fprintf(stderr, "fail to BIO_read\n");return -1;}BIO_free_all(b64);return 0;
}

下面是通過編解碼字符串的測試代碼：

int test_openssl_base64_simple()
{const char* src = "https://blog.csdn.net/fengbingchun https://github.com//fengbingchun";int inlen = strlen(src);int outlen = (inlen + 2) / 3 * 4 + ((inlen + 2) / 3 * 4 + 63) / 64;std::unique_ptr<char[]> out1(new char[outlen]);bool newline = true;int ret = openssl_base64_encode((const unsigned char*)src, inlen, out1.get(), &outlen, newline);if (ret != 0) {fprintf(stderr, "fail to openssl_base64_encode\n");return -1;}fprintf(stdout, "encode result:\n");std::for_each(out1.get(), out1.get() + outlen, [](char& c) { fprintf(stdout, "%c", c); });fprintf(stdout, "\n");std::unique_ptr<unsigned char[]> dst(new unsigned char[outlen]);int outlen1 = 0;ret = openssl_base64_decode(out1.get(), outlen, dst.get(), &outlen1, newline);if (ret != 0) {fprintf(stderr, "fail to openssl_base64_decode\n");return -1;}fprintf(stdout, "decode result:\n");std::for_each(dst.get(), dst.get() + outlen1, [](unsigned char& c) { fprintf(stdout, "%c", (char)c); });fprintf(stdout, "\n");dst[outlen1] = '\0';if (strcmp(src, (const char*)dst.get()) == 0) {fprintf(stdout, "test success\n");return 0;} else {fprintf(stdout, "test fail\n");return -1;}
}

執行結果如下圖所示：

之前在https://blog.csdn.net/fengbingchun/article/details/106546012中使用OpenSSL的函數PEM_read_RSAPrivateKey直接對pem文件進行解析，下面測試代碼是通過調用上面的base64解碼函數實現的解析：

int test_openssl_base64_complex()
{
#ifdef _MSC_VERconst char* name = "E:/GitCode/OpenSSL_Test/testdata/rsa_private.pem";
#elseconst char* name = "testdata/rsa_private.pem";
#endifconst char* begin = "-----BEGIN RSA PRIVATE KEY-----";const char* end = "-----END RSA PRIVATE KEY-----";FILE *fp = fopen(name, "rb");if (!fp) {fprintf(stderr, "fail to open file: %s\n", name);return -1;}fseek(fp, 0, SEEK_END);long length = ftell(fp);rewind(fp);std::unique_ptr<unsigned char[]> data(new unsigned char[length]);fread(data.get(), 1, length, fp);fclose(fp);const char* p1 = strstr((const char*)data.get(), begin);if (!p1) {fprintf(stderr, "it's not a pem file: %s\n", name);return -1;}const char* p2 = strstr((const char*)data.get(), end);if (!p2) {fprintf(stderr, "it's not a pem file: %s\n", name);return -1;}bool newline = true;long length2 = p2 - p1;std::unique_ptr<unsigned char[]> decoded(new unsigned char[length2]);int outlen = 0;int ret = openssl_base64_decode(p1 + strlen(begin) + 1, length2, decoded.get(), &outlen, newline); // + 一個換行符長度const unsigned char* p = decoded.get();RSA_PRIVATE_KEY* key = d2i_RSA_PRIVATE_KEY(nullptr, &p, outlen);if (!key) {fprintf(stderr, "fail to d2i_RSA_PRIVATE_KEY\n");return -1;}print(key->version, "version");print(key->n, "n");print(key->e, "e");print(key->d, "d");print(key->p, "p");print(key->q, "q");print(key->exp1, "exp1");print(key->exp2, "exp2");print(key->coeff, "coeff");RSA_PRIVATE_KEY_free(key);return 0;
}

執行結果如下：與直接使用PEM_read_RSAPrivateKey得到的結果是一致的

以上代碼段的完整code見：GitHub/OpenSSL_Test

GitHub：https://github.com/fengbingchun/OpenSSL_Test

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