使用BIGNUM库验证数字签名

Question

为什么我的代码返回奇怪的结果？

void printBN(char *msg, BIGNUM * a)
{
    char * number_str = BN_bn2hex(a);
    printf("%s %s\n", msg, number_str);
    OPENSSL_free(number_str);
}

int main () 
{
    BN_CTX *ctx = BN_CTX_new();

    BIGNUM *e = BN_new();
    BIGNUM *n = BN_new();
    BIGNUM *d = BN_new();
    BIGNUM *plaintxt = BN_new();
    BIGNUM *signature = BN_new();

    BN_hex2bn(&signature, "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");
    BN_hex2bn(&n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
    BN_hex2bn(&e, "10001");

    BN_mod_exp(plaintxt, signature, e, n, ctx);
    printBN("hash value: \n", plaintxt);

}

我的代码给出了以下结果，看起来不像是正确的计算结果：

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

Answer 1

看起来像是正确的结果，除了您缺少起始字节，因为它是defined（PKCS＃1 v2.2）为00：

标题字节：

01

PKCS＃1 v1.5填充字符：

FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

填充字符结尾：

00

ASN.1哈希OID和哈希值的编码：

3031300D060960864801650304020105000420BC5F9353CBB9DCAE86B9F8F68C1C95856DB836ACA2E00C9319716CDF4DD0F5

[decodes（Lapo的ASN.1解码器）：

SEQUENCE (2 elem)
  SEQUENCE (2 elem)
    OBJECT IDENTIFIER 2.16.840.1.101.3.4.2.1 sha-256 (NIST Algorithm)
    NULL
  OCTET STRING (32 byte) BC5F9353CBB9DCAE86B9F8F68C1C95856DB836ACA2E00C9319716CDF4DD0F5BA

八位字节串的内容（十六进制的字节数组）是哈希值。

---

我想这比您最初想象的要复杂一些。尝试PSS，它甚至更复杂（但也更安全）。请注意，有many attacks on "raw" or "textbook" RSA（仅是模幂）。要求此类填充具有安全签名，或者-如果是加密，则具有密文。