Add optional support for AEGIS encryption

AEGIS is a new family of authenticated encryption algorithms that offers
stronger security, higher usage limits, and better performance than AES-GCM.

This pull request adds support for a new `-aegis` command-line flag, allowing
AEGIS-128X2 to be used as an alternative to AES-GCM on CPUs with AES acceleration.

It also introduces the ability to use ciphers with different key sizes.

More information on AEGIS is available here:
- https://cfrg.github.io/draft-irtf-cfrg-aegis-aead/draft-irtf-cfrg-aegis-aead.html
- https://github.com/cfrg/draft-irtf-cfrg-aegis-aead

gocryptfs -speed speed on Apple M1:

AES-GCM-256-OpenSSL              3718.79 MB/s
AES-GCM-256-Go                   5083.43 MB/s   (selected in auto mode)
AES-SIV-512-Go                    625.20 MB/s
XChaCha20-Poly1305-OpenSSL       1358.63 MB/s   (selected in auto mode)
XChaCha20-Poly1305-Go             832.11 MB/s
Aegis128X2-Go                   11818.73 MB/s

gocryptfs -speed speed on AMD Zen 4:

AES-GCM-256-OpenSSL              5215.86 MB/s
AES-GCM-256-Go                   6918.01 MB/s   (selected in auto mode)
AES-SIV-512-Go                    449.61 MB/s
XChaCha20-Poly1305-OpenSSL       2643.48 MB/s
XChaCha20-Poly1305-Go            3727.46 MB/s   (selected in auto mode)
Aegis128X2-Go                   28109.92 MB/s

1 files changed, 8 insertions, 1 deletions

diff --git a/internal/speed/speed.go b/internal/speed/speed.go
index d6fa12e..e60e37d 100644
--- a/internal/speed/speed.go
+++ b/internal/speed/speed.go
@@ -47,13 +47,14 @@ func Run() {
 		{name: cryptocore.BackendAESSIV.String(), f: bAESSIV, preferred: false},
 		{name: cryptocore.BackendXChaCha20Poly1305OpenSSL.String(), f: bStupidXchacha, preferred: stupidgcm.PreferOpenSSLXchacha20poly1305()},
 		{name: cryptocore.BackendXChaCha20Poly1305.String(), f: bXchacha20poly1305, preferred: !stupidgcm.PreferOpenSSLXchacha20poly1305()},
+		{name: cryptocore.BackendAegis.String(), f: bAegis, preferred: false},
 	}
 	testing.Init()
 	for _, b := range bTable {
 		fmt.Printf("%-26s\t", b.name)
 		mbs := mbPerSec(testing.Benchmark(b.f))
 		if mbs > 0 {
-			fmt.Printf("%7.2f MB/s", mbs)
+			fmt.Printf("%8.2f MB/s", mbs)
 		} else {
 			fmt.Printf("    N/A")
 		}
@@ -168,3 +169,9 @@ func bStupidXchacha(b *testing.B) {
 	}
 	bEncrypt(b, stupidgcm.NewXchacha20poly1305(randBytes(32)))
 }
+
+// bAegis benchmarks Aegis from github.com/aegis-aead/go-libaegis
+func bAegis(b *testing.B) {
+	c := stupidgcm.NewAegis(randBytes(16))
+	bEncrypt(b, c)
+}