51 lines
1.2 KiB
Go
51 lines
1.2 KiB
Go
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// Package fingerprint provides a helper to create fingerprint string from certificate
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package fingerprint
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import (
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"crypto"
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"crypto/x509"
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"errors"
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"fmt"
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)
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var (
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errHashUnavailable = errors.New("fingerprint: hash algorithm is not linked into the binary")
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errInvalidFingerprintLength = errors.New("fingerprint: invalid fingerprint length")
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)
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// Fingerprint creates a fingerprint for a certificate using the specified hash algorithm
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func Fingerprint(cert *x509.Certificate, algo crypto.Hash) (string, error) {
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if !algo.Available() {
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return "", errHashUnavailable
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}
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h := algo.New()
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for i := 0; i < len(cert.Raw); {
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n, _ := h.Write(cert.Raw[i:])
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// Hash.Writer is specified to be never returning an error.
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// https://golang.org/pkg/hash/#Hash
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i += n
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}
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digest := []byte(fmt.Sprintf("%x", h.Sum(nil)))
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digestlen := len(digest)
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if digestlen == 0 {
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return "", nil
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}
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if digestlen%2 != 0 {
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return "", errInvalidFingerprintLength
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}
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res := make([]byte, digestlen>>1+digestlen-1)
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pos := 0
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for i, c := range digest {
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res[pos] = c
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pos++
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if (i)%2 != 0 && i < digestlen-1 {
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res[pos] = byte(':')
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pos++
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}
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}
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return string(res), nil
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}
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