c++ - 如何使用 Openssl 编码 ASN.1 上下文特定

Question

我正在尝试对 pkcs7 封装的内容信息进行编码:

Sequence:
  OID
  [0] Context-specific
     OCTET STRING

我的第一个问题是编码特定上下文:

[0] Context-specific

所以我尝试用“Octet String”创建一个“SET Context-specific”，但没有成功:

// Create ASN1_OCTET
ASN1_OCTET_STRING *obj = ASN1_OCTET_STRING_new();
const BYTE* ptr = dataToSign.getData();
ASN1_OCTET_STRING_set(obj, ptr, dataToSign.getSize());

// Create ASN1_TYPE using ASN1_OCTET
ASN1_TYPE   *asn1Type   = ASN1_TYPE_new();
asn1Type->type = V_ASN1_OCTET_STRING;
asn1Type->value.octet_string = obj;

// Using i2d_ASN1_SET_OF_ASN1_TYPE
stack_st_ASN1_TYPE* sk = sk_ASN1_TYPE_new_null();
sk_ASN1_TYPE_push(sk,asn1Type);
int tamanho = i2d_ASN1_SET_OF_ASN1_TYPE(sk,(unsigned char **) NULL, i2d_ASN1_TYPE,V_ASN1_SET, V_ASN1_CONTEXT_SPECIFIC, IS_SET);
unsigned char* data = new BYTE[tamanho];
tamanho = i2d_ASN1_SET_OF_ASN1_TYPE(sk,(unsigned char **) &data, i2d_ASN1_TYPE,V_ASN1_SET, V_ASN1_CONTEXT_SPECIFIC, IS_SET);

我在openssl的网站上没有找到文档.这个地方比较好umich - Openssl documentation

我走在正确的轨道上吗？

Answer 1

使用 i2d_ASN1_bytes 函数:

// Initialize ASN1_STRING inplace (no need to free)
ASN1_STRING s = { 0, 0, NULL, 0};
// Initialize with our data
ASN1_STRING_set0(&obj, dataToSign.getData(), dataToSign.getSize());

// Get resulting object length
int data_len = i2d_ASN1_bytes(obj, NULL, 0, V_ASN1_CONTEXT_SPECIFIC)
// Encode object with context tag 0
unsigned char* data = new BYTE[data_len];
unsigned char* p = data;
i2d_ASN1_bytes(obj, &p, 0, V_ASN1_CONTEXT_SPECIFIC);