openssl rust crate：ECDSA 签名大小不是 64 字节？

Question

我想使用OpenSSL rust crate to perform cryptography operations, specifically using the ECDSA算法。

我使用以下代码生成 ECDSA 密钥（椭圆曲线 P-256）并使用它来签署数据并获得签名：

    use openssl::sign::{Signer, Verifier};
    use openssl::ec::{EcKey, EcGroup};
    use openssl::pkey::PKey;
    use openssl::hash::MessageDigest;
    use openssl::nid::Nid;

    // ec key
    let group = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
    let keypair = EcKey::generate(&group).unwrap();
    let keypair = PKey::from_ec_key(keypair).unwrap();

    // data to sign
    let data = b"hello, world!";

    // hash: sha-256
    let mut signer = Signer::new(MessageDigest::sha256(), &keypair).unwrap();
    let buf_size = signer.len().unwrap();  // Computes an upper bound on the signature length.
    println!("buffer size {}", buf_size);  // 72
    let mut buf: [u8; 72] = [0; 72];

    // sign
    let exact_bytes = signer.sign_oneshot(&mut buf, data).unwrap(); //the number of bytes written.
    println!("{}", exact_bytes); // 70

我不明白为什么 exact_bytes 是 70。在我的理解中，it should be 64。

ECDSA signatures are 2 times longer than the signer's private key for the curve used during the signing process. For example, for 256-bit elliptic curves (like secp256k1) the ECDSA signature is 512 bits (64 bytes) and for 521-bit curves (like secp521r1) the signature is 1042 bits.

有什么帮助吗？谢谢！

Answer 1

从here看来，它似乎也取决于签名使用的编码，这可能会增加长度。

另外，说明了你对签名长度的理解，和你说的不太一样

openssl rust crate：ECDSA 签名大小不是 64 字节？

openssl rust crate: ECDSA signature size is not 64 bytes?

openssl

digital-signature

rust

ecdsa