英文:
Converting *crypto.PrivateKey to *rsa.PrivateKey
问题
我正在开发一种根据传入的私钥类型生成签名的方法。为了做到这一点，我将一个 *crypto.PrivateKey 变量作为参数传递。但是当我想要进行类型断言以使用该参数时，问题就出现了。
func Sign(text string, privKey *crypto.PrivateKey) string{
if _, ok := (*privKey).(rsa.PrivateKey) //这样是可以的
if _, ok := (privKey).(*rsa.PrivateKey) //这样是不可以的
我猜我可以做第一种方式，因为如果我使用"*"，编译器会认为它是一个接口。但是我不知道为什么我不能做第二种方式，当它应该是正确的时候。
顺便说一下，我需要使用一个 *rsa.PrivateKey 类型的变量，我可以这样做：
privRsa, _ := (*privKey).(rsa.PrivateKey)
var priv *rsa.PrivateKey
priv = &privRsa
我无法理解的是为什么我不能直接将 *crypto.PrivateKey 转换为 *rsa.PrivateKey，或者是否存在一种方法可以做到这一点。我认为，按照我目前的做法，这样做会在内存中分配新的空间，如果我希望它高效，就不应该这样做。
英文:
I am developing a method that will make a signature based in the type of private key that is passed as argument. To do that, I'm passing a *crypto.PrivateKey variable as argument. But the problem comes when I want to do a type assertion to use the argument.
func Sign(text string, privKey *crypto.PrivateKey) string{
if _, ok := (*privKey).(rsa.PrivateKey) //This is ok
if _, ok := (privKey).(*rsa.PrivateKey) //This is not ok 2
I guess I can do the first thing because if I use "*", the compiler think that it is an interface. But I don't know why I can't do the second thing, when it should be correct.
By the way, I need to use a variable of type *rsa.PrivateKey, I can do this this way:
privRsa, _ := (*privKey).(rsa.PrivateKey)
var priv *rsa.PrivateKey
priv = &privRsa
What I can not understand is why I can't directly convert the *crypto.PrivateKey into *rsa.PrivateKey, or if it exist a way to do that. I thing doing it the way I'm doing it right now would allocate new space in memory that I shouldn't if I want it to be efficient
答案1
得分: 1
crypto.PrivateKey 是一个接口。*crypto.PrivateKey 是一个指向接口的指针。你可以在接口上使用类型断言来获取底层值：
func Sign(text string, privKey crypto.PrivateKey) string {
if _, ok := privKey.(rsa.PrivateKey); ok {
// ...
}
}
// ...
var pkey rsa.PrivateKey
Sign(text, pkey)
在这里，接口中的私钥值是 rsa.PrivateKey 的一个副本。
如果你传递 pkey 的地址，那么接口将持有私钥的指针：
func Sign(text string, privKey crypto.PrivateKey) string {
if _, ok := privKey.(*rsa.PrivateKey); ok {
// ...
}
}
// ...
var pkey rsa.PrivateKey
Sign(text, &pkey)
英文:
crypto.PrivateKey is an interface. *crypto.PrivateKey is a pointer to an interface. You can use type-assertion on an interface to get the underlying value:
func Sign(text string, privKey crypto.PrivateKey) string{
if _, ok := privKey.(rsa.PrivateKey)
...
}
...
var pkey rsa.PrivateKey
Sign(text,pkey)
Here, the private key value in the interface is a copy of the rsa.PrivateKey.
If you pass the address of pkey, then, then the interface would have a pointer to the private key:
func Sign(text string, privKey crypto.PrivateKey) string{
if _, ok := privKey.(*rsa.PrivateKey)
...
}
...
var pkey rsa.PrivateKey
Sign(text,&pkey)
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