open-consul/agent/connect/common_names.go

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package connect
import (
"crypto/rand"
"encoding/binary"
"fmt"
"regexp"
"strconv"
"strings"
)
var invalidDNSNameChars = regexp.MustCompile(`[^a-z0-9]`)
// ServiceCN returns the common name for a service's certificate. We can't use
// SPIFFE URIs because some CAs require valid FQDN format. We can't use SNI
// values because they are often too long than the 64 bytes allowed by
// CommonNames. We could attempt to encode more information into this to make
// identifying which instance/node it was issued to in a management tool easier
// but that just introduces more complications around length. It's also strange
// that the Common Name would encode more information than the actual
// identifying URI we use to assert anything does and my lead to bad assumptions
// that the common name is in some way "secure" or verified - there is nothing
// inherently provable here except that the requestor had ACLs for that service
// name in that DC.
//
// Format is:
// <sanitized_service_name>.svc.<trust_domain_first_8>.consul
//
// service name is sanitized by removing any chars that are not legal in a DNS
// name and lower casing. It is truncated to the first X chars to keep the
// total at 64.
//
// trust domain is truncated to keep the whole name short
func ServiceCN(serviceName, trustDomain string) string {
svc := invalidDNSNameChars.ReplaceAllString(strings.ToLower(serviceName), "")
// 20 = 7 bytes for ".consul", 8 bytes for trust domain, 5 bytes for ".svc."
return fmt.Sprintf("%s.svc.%s.consul",
truncateTo(svc, 64-20), truncateTo(trustDomain, 8))
}
// AgentCN returns the common name for an agent certificate. See ServiceCN for
// more details on rationale.
//
// Format is:
// <sanitized_node_name>.agnt.<trust_domain_first_8>.consul
//
// node name is sanitized by removing any chars that are not legal in a DNS
// name and lower casing. It is truncated to the first X chars to keep the
// total at 64.
//
// trust domain is truncated to keep the whole name short
func AgentCN(node, trustDomain string) string {
nodeSan := invalidDNSNameChars.ReplaceAllString(strings.ToLower(node), "")
// 21 = 7 bytes for ".consul", 8 bytes for trust domain, 6 bytes for ".agnt."
return fmt.Sprintf("%s.agnt.%s.consul",
truncateTo(nodeSan, 64-21), truncateTo(trustDomain, 8))
}
// CompactUID returns a crypto random Unique Identifier string consiting of 8
// characters of base36 encoded random value. This has roughly 41 bits of
// entropy so is suitable for infrequently occuring events with low probability
// of collision. It is not suitable for UUIDs for very frequent events. It's
// main purpose is to assign unique values to CA certificate Common Names which
// need to be unique in some providers - see CACN - but without using up large
// amounts of the limited 64 character Common Name. It also makes the values
// more easily digestable by humans considering there are likely to be few of
// them ever in use.
func CompactUID() (string, error) {
// 48 bits (6 bytes) is enough to fill 8 bytes in base36 but it's simpler to
// have a whole uint8 to convert from.
var raw [8]byte
_, err := rand.Read(raw[:])
if err != nil {
return "", err
}
i := binary.LittleEndian.Uint64(raw[:])
return truncateTo(strconv.FormatInt(int64(i), 36), 8), nil
}
// CACN returns the common name for a CA certificate. See ServiceCN for more
// details on rationale. A uniqueID is requires because some providers (e.g.
// Vault) cache by subject and so produce incorrect results - for example they
// won't cross-sign an older CA certificate with the same common name since they
// think they already have a valid cert for that CN and just return the current
// root.
//
// This can be generated by any means but will be truncated to 8 chars and
// sanitised to DNS-safe chars. CompactUID generates suitable UIDs for this
// specific purpose.
//
// Format is:
// {provider}-{uniqueID_first8}.{pri|sec}.ca.<trust_domain_first_8>.consul
//
// trust domain is truncated to keep the whole name short
func CACN(provider, uniqueID, trustDomain string, primaryDC bool) string {
providerSan := invalidDNSNameChars.ReplaceAllString(strings.ToLower(provider), "")
typ := "pri"
if !primaryDC {
typ = "sec"
}
// 32 = 7 bytes for ".consul", 8 bytes for trust domain, 8 bytes for
// ".pri.ca.", 9 bytes for "-{uniqueID-8-b36}"
uidSAN := invalidDNSNameChars.ReplaceAllString(strings.ToLower(uniqueID), "")
return fmt.Sprintf("%s-%s.%s.ca.%s.consul", typ, truncateTo(uidSAN, 8),
truncateTo(providerSan, 64-32), truncateTo(trustDomain, 8))
}
func truncateTo(s string, n int) string {
if len(s) > n {
return s[:n]
}
return s
}
// CNForCertURI returns the correct common name for a given cert URI type. It
// doesn't work for CA Signing IDs since more context is needed and CA Providers
// always know their CN from their own context.
func CNForCertURI(uri CertURI) (string, error) {
// Even though leafs should be from our own CSRs which should have the same CN
// logic as here, override anyway to account for older version clients that
// didn't include the Common Name in the CSR.
switch id := uri.(type) {
case *SpiffeIDService:
return ServiceCN(id.Service, id.Host), nil
case *SpiffeIDAgent:
return AgentCN(id.Agent, id.Host), nil
case *SpiffeIDSigning:
return "", fmt.Errorf("CertURI is a SpiffeIDSigning, not enough context to generate Common Name")
default:
return "", fmt.Errorf("CertURI type not recognized")
}
}