使用 openssl C API 构建 ASN1 集

Question

我正在尝试使用 openssl C API 构建一组序列。正如在各个地方所指出的那样，这方面的文档非常稀少，而且代码示例似乎不存在。

我在网上找到了各种建议，但没有一个似乎能正常工作。

为了创建序列，我已经做到了这一点：

#include <openssl/asn1t.h>

countdef struct StringStructure {
    ASN1_INTEGER *count;
    ASN1_INTEGER *asnVersion;
    ASN1_OCTET_STRING *value;
} StringSequence;

DECLARE_ASN1_FUNCTIONS(StringSequence)

ASN1_SEQUENCE(StringSequence) = {
    ASN1_SIMPLE(StringSequence, count, ASN1_INTEGER),
    ASN1_SIMPLE(StringSequence, asnVersion, ASN1_INTEGER),
    ASN1_SIMPLE(StringSequence, value, ASN1_OCTET_STRING),
} ASN1_SEQUENCE_END(StringSequence)

IMPLEMENT_ASN1_FUNCTIONS(StringSequence)

auto aSeq = StringSequence_new();
aSeq->count = ASN1_INTEGER_new();
aSeq->asnVersion = ASN1_INTEGER_new();
aSeq->value = ASN1_OCTET_STRING_new();
if (!ASN1_INTEGER_set(aSeq->count, 10) ||
    !ASN1_INTEGER_set(aSeq->asnVersion, 1) ||
    !ASN1_STRING_set(aSeq->value, "Test", -1)) {
    // -- Error
}

auto anotherSeq = StringSequence_new();
anotherSeq->count = ASN1_INTEGER_new();
anotherSeq->asnVersion = ASN1_INTEGER_new();
anotherSeq->value = ASN1_OCTET_STRING_new();
if (!ASN1_INTEGER_set(anotherSeq->count, 32) ||
    !ASN1_INTEGER_set(anotherSeq->asnVersion, 1) ||
    !ASN1_STRING_set(anotherSeq->value, "Something Else", -1)) {
    // -- Error
}

我从那里去哪里才能构建一组这些？

Answer 1

OpenSSL 源代码是您最好的文档...

作为您尝试构建的构造示例，请查看the PKCS7_SIGNED ASN1 definition in crypto/pkcs7/pk7_asn1.c：

ASN1_NDEF_SEQUENCE(PKCS7_SIGNED) = {
        ASN1_SIMPLE(PKCS7_SIGNED, version, ASN1_INTEGER),
        ASN1_SET_OF(PKCS7_SIGNED, md_algs, X509_ALGOR),
        ASN1_SIMPLE(PKCS7_SIGNED, contents, PKCS7),
        ASN1_IMP_SEQUENCE_OF_OPT(PKCS7_SIGNED, cert, X509, 0),
        ASN1_IMP_SET_OF_OPT(PKCS7_SIGNED, crl, X509_CRL, 1),
        ASN1_SET_OF(PKCS7_SIGNED, signer_info, PKCS7_SIGNER_INFO)
} ASN1_NDEF_SEQUENCE_END(PKCS7_SIGNED)

它的第二个成员md_algs是一组X509_ALGOR，它本身就是a sequence defined in crypto/asn1/x_algor.c：

ASN1_SEQUENCE(X509_ALGOR) = {
        ASN1_SIMPLE(X509_ALGOR, algorithm, ASN1_OBJECT),
        ASN1_OPT(X509_ALGOR, parameter, ASN1_ANY)
} ASN1_SEQUENCE_END(X509_ALGOR)

因此，md_algs 字段是一组序列，就像您要求的那样。等效的 C 结构定义可以在include/openssl/pkcs7.h 中找到：

typedef struct pkcs7_signed_st {
    ASN1_INTEGER *version;      /* version 1 */
    STACK_OF(X509_ALGOR) *md_algs; /* md used */
    STACK_OF(X509) *cert;       /* [ 0 ] */
    STACK_OF(X509_CRL) *crl;    /* [ 1 ] */
    STACK_OF(PKCS7_SIGNER_INFO) *signer_info;
    struct pkcs7_st *contents;
} PKCS7_SIGNED;

md_algs 字段表明，要捕获集合构造，您需要使用旨在处理集合的the STACK API。在您的情况下，这将是 STACK_OF(StringSequence)。