// Optimal chains are the shortest chains, with newest intermediates and most advanced crypto suite being the tie breaker.
func optimalChains(chains [][]*x509.Certificate) [][]*x509.Certificate {
// Find shortest chains
chains = ubiquity.Filter(chains, ubiquity.CompareChainLength)
// Find the chains with longest expiry.
chains = ubiquity.Filter(chains, ubiquity.CompareChainExpiry)
// Find the chains with more advanced crypto suite
chains = ubiquity.Filter(chains, ubiquity.CompareChainCryptoSuite)
return chains
}
// Force chains returns the input bundle (plus one verified root CA) as the highest ranked ones if possible.
// If there doesn't exist such bundle, fall back to the most ubiquitous bundle.
func forceChains(input []*x509.Certificate, chains [][]*x509.Certificate) [][]*x509.Certificate {
// Filter out chains that are the same as the input certs.
var candidateChains [][]*x509.Certificate
for _, chain := range chains {
if !diff(chain[:len(chain)-1], input) {
candidateChains = append(candidateChains, chain)
}
}
if len(candidateChains) == 0 {
candidateChains = chains
}
// Filter out chains with highest cross platform ubiquity.
return ubiquity.Filter(candidateChains, ubiquity.ComparePlatformUbiquity)
}
// Ubiquitous chains are the chains with highest platform coverage and break ties with the optimal strategy.
func ubiquitousChains(chains [][]*x509.Certificate) [][]*x509.Certificate {
// Filter out chains with highest cross platform ubiquity.
chains = ubiquity.Filter(chains, ubiquity.ComparePlatformUbiquity)
// Prefer that all intermediates are SHA-2 certs if the leaf is a SHA-2 cert, in order to improve ubiquity.
chains = ubiquity.Filter(chains, ubiquity.CompareSHA2Homogeneity)
// Filter shortest chains
chains = ubiquity.Filter(chains, ubiquity.CompareChainLength)
// Filter chains with highest signature hash ubiquity.
chains = ubiquity.Filter(chains, ubiquity.CompareChainHashUbiquity)
// Filter chains with highest keyAlgo ubiquity.
chains = ubiquity.Filter(chains, ubiquity.CompareChainKeyAlgoUbiquity)
// Filter chains with intermediates that last longer.
chains = ubiquity.Filter(chains, ubiquity.CompareExpiryUbiquity)
// Use the optimal strategy as final tie breaker.
return optimalChains(chains)
}