OpenSSL ECDSA 签名比预期的要长 [英] OpenSSL ECDSA signatures longer than expected

问题描述

我正在尝试生成用于加密芯片的原始"、未编码的 ECDSA 签名.目标是在主机 PC 上签名，然后将其发送到芯片进行验证.但是，我遇到了一个小问题.我的理解是 ECDSA 签名应该是 64 字节(对于 secp256v1).而且，当我使用芯片生成签名时，它的长度确实是 64 字节.但是，当我使用 openssl 时，签名的长度为 71 个字节.签名的开头似乎是某种前缀，但我找不到任何关于它是什么的数据.

这是我尝试做所有事情的方式:

生成密钥:

openssl ecparam -genkey -name secp256r1 -noout -out privkeyv1.pem

生成要签名的消息":

echo -n "Hello World" >测试.txt

我尝试了两种方法来签署消息.两者都会导致相同的意外输出.

第一种方法——生成测试文件的sha256哈希，然后签名:

sha256sum test.txt |剪切 -f 1 -d " " >哈希

使用 pkutil 签名

openssl pkeyutl -sign -in hash -inkey privkeyv1.pem -out test_sig_meth1

方法二:使用 openssl dgst 签名

openssl dgst -sha256 -binary -sign privkeyv1.pem -out test_sig_meth2 test.txt问题:这是 xxd -p -c 256 test_sig_meth1 的输出:3045022000a86fb146d5f8f6c15b962640bc2d1d928f5e0f96a5924e4db2853ec8b66fb002210085431613d0a235db1adabc090cc1062a246a78941972e2984b84f>dp84823

以及xxd -p -c 256 test_sig_meth2的输出:30450220693732cd53d9f2ba3deae213d74cdf69a00e7325a10ddc6a4445ff2b33f95e62022100b6d2561e3afba10f95247ed05f0c59620dc0913f0d798b6348e05c>e>1e

如您所见，这两种方法都会在开头生成一些看起来像头字节的字节(30450220，可能更长)，但我不确定它们的用途或方法删除它们.作为参考，这里是在加密芯片上生成的相同方法的签名.如果您在末尾删除空字节填充，则为 64 个字节.<代码>4677AD09F2AF49D7445ED5D6AC7253ADC863EC6D5DB6D3CFBF9C6D3E221D0A7BA2561942524F46B590AEE749D827FBF80A961E884E3A7D85EC75FE48ADBC0BD000000000000000000000000000000

问题:如何使用 openssl 生成一个 64 字节的原始(未编码，没有标头)ECDSA 签名，我可以在这个方案中使用?

解决方案

出于效率原因，大多数芯片只会将 r 和 s 输出为字节数组或八位字节字符串，其中每个 r 和 s 与八位字节中的字段大小(即密钥大小)相同.另一种方法是将 r 和 s 输出为一个数字序列，因为最后，这就是 r 和 s 是.使用 ASN.1，这将成为 INTEGER 值的序列.

要从这样的序列转换，您可以首先使用 BER 解析器进行 BER 解码以检索整数.然后实现一个 I2OSP 算法(整数到八位字节流原语)，它需要以字节/八位字节为单位的值和密钥大小作为参数.该数字应该是大整数形式，但这很好，因为 ASN.1 BER 编码的整数也是大整数.如果数字太小，基本上你必须用零字节填充.然后你连接数字.

我不会进入将字节数组转换为整数的 OS2IP.请注意，如果您以 BER 形式对其进行编码，那么整数应该 not 用零字节填充.所以还是需要一些诡计的.

所以虽然签名改变了形式，但签名仍然有效；您可以简单地在一种形式和另一种形式之间进行转换，并且签名仍然会验证 - 显然，只要您使用正确的库来完成这项工作.

I am attempting to generate "raw", unencoded ECDSA signatures for use with a cryptographic chip. The goal is to sign something on the host pc, then send it to the chip to be validated. However, I am running into a little problem. My understanding is that the ECDSA signature should be 64 bytes (for secp256v1). And, when I use the chip to generate a signature, it is indeed 64 bytes in length. However, when I use openssl, the signature is 71 bytes in length. The beginning of the signature seems to be some kind of prefix, but I can't find any data about what that is.

Here is how I am trying to do everything:

Generate the key:

openssl ecparam -genkey -name secp256r1 -noout -out privkeyv1.pem

Generate the "message" to be signed:

echo -n "Hello World" > test.txt

I have tried two methods for signing the message. Both lead to the same, unexpected output.

First method - generate sha256 hash of test file, then sign it:

sha256sum test.txt | cut -f 1 -d " " > hash

Sign with pkutil

openssl pkeyutl -sign -in hash -inkey privkeyv1.pem -out test_sig_meth1

Method 2: Sign with openssl dgst

openssl dgst -sha256 -binary -sign privkeyv1.pem -out test_sig_meth2 test.txt The issue: Here is the output of xxd -p -c 256 test_sig_meth1: 3045022000a86fb146d5f8f6c15b962640bc2d1d928f5e0f96a5924e4db2853ec8b66fb002210085431613d0a235db1adabc090cc1062a246a78941972e298423f4b3d081b48c8

And the output of xxd -p -c 256 test_sig_meth2: 30450220693732cd53d9f2ba3deae213d74cdf69a00e7325a10ddc6a4445ff2b33f95e62022100b6d2561e3afba10f95247ed05f0c59620dc0913f0d798b4148e05c4116b6384e

As you can see, both of these methods generate some bytes at the beginning that look like header bytes (the 30450220, maybe longer), but I am not sure what they are for or how to remove them. For reference, here is a a signature of the same method generated on the crypto chip. If you remove the null byte padding at the end, it's 64 bytes. 4677AD09F2AF49D7445ED5D6AC7253ADC863EC6D5DB6D3CFBF9C6D3E221D0A7BA2561942524F46B590AEE749D827FBF80A961E884E3A7D85EC75FE48ADBC0BD00000000000000000000000

The question: How can I use openssl to generate a 64 byte raw (unencoded, with no header) ECDSA signature I can use with this scheme?

解决方案

Most chips will, for efficiency reasons, just output the r and s as a byte array or octet string, where each r and s is the same as the field size (i.e. key size) in octets. Another approach is to output r and s as a sequence of numbers, because in the end, that is what r and s are. Using ASN.1 this becomes a SEQUENCE of INTEGER values.

To convert from such a sequence you can first BER decode using a BER parser to retrieve the integer. Then implement an I2OSP algorithm (integer to octet stream primitive) which requires the value and the key size in bytes/octets as arguments. The number should be in big integer form, but that's fine as ASN.1 BER encoded integers are also big integers. Basically you must left pad with zero bytes if the number is too small. Then you concatenate the number.

I won't go into OS2IP which converts a byte array to an integer. Note thought that if you encode it in BER form then the integers should not be left padded with zero bytes. So some trickery is required still.

So although the signature changes form, the signature still stays valid; you can simply convert between one form and the other and the signature will still verify - as long as you use the right library for the job, obviously.

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