stupidgcm: introduce stupidAEADCommon and use for both chacha & gcm

Nice deduplication and brings the GCM decrypt speed up to par.

internal/speed$ benchstat old new
name                old time/op   new time/op   delta
StupidGCM-4          4.71µs ± 0%   4.66µs ± 0%   -0.99%  (p=0.008 n=5+5)
StupidGCMDecrypt-4   5.77µs ± 1%   4.51µs ± 0%  -21.80%  (p=0.008 n=5+5)

name                old speed     new speed     delta
StupidGCM-4         870MB/s ± 0%  879MB/s ± 0%   +1.01%  (p=0.008 n=5+5)
StupidGCMDecrypt-4  710MB/s ± 1%  908MB/s ± 0%  +27.87%  (p=0.008 n=5+5)

1 files changed, 108 insertions, 0 deletions

diff --git a/internal/stupidgcm/openssl.go b/internal/stupidgcm/openssl.go
new file mode 100644
index 0000000..d57d100
--- /dev/null
+++ b/internal/stupidgcm/openssl.go
@@ -0,0 +1,108 @@
+package stupidgcm
+
+import (
+	"fmt"
+	"log"
+)
+
+/*
+#include "openssl_aead.h"
+#cgo pkg-config: libcrypto
+*/
+import "C"
+
+func openSSLSeal(a *stupidAEADCommon, dst, iv, in, authData []byte) []byte {
+	if a.Wiped() {
+		panic("BUG: tried to use wiped key")
+	}
+	if len(iv) != a.NonceSize() {
+		log.Panicf("Only %d-byte IVs are supported, you passed %d bytes", a.NonceSize(), len(iv))
+	}
+	if len(in) == 0 {
+		log.Panic("Zero-length input data is not supported")
+	}
+
+	// If the "dst" slice is large enough we can use it as our output buffer
+	outLen := len(in) + tagLen
+	var buf []byte
+	inplace := false
+	if cap(dst)-len(dst) >= outLen {
+		inplace = true
+		buf = dst[len(dst) : len(dst)+outLen]
+	} else {
+		buf = make([]byte, outLen)
+	}
+
+	res := int(C.openssl_aead_seal(a.openSSLEVPCipher,
+		(*C.uchar)(&in[0]),
+		C.int(len(in)),
+		(*C.uchar)(&authData[0]),
+		C.int(len(authData)),
+		(*C.uchar)(&a.key[0]),
+		C.int(len(a.key)),
+		(*C.uchar)(&iv[0]),
+		C.int(len(iv)),
+		(*C.uchar)(&buf[0]),
+		C.int(len(buf))))
+
+	if res != outLen {
+		log.Panicf("expected length %d, got %d", outLen, res)
+	}
+
+	if inplace {
+		return dst[:len(dst)+outLen]
+	}
+	return append(dst, buf...)
+}
+
+func openSSLOpen(a *stupidAEADCommon, dst, iv, in, authData []byte) ([]byte, error) {
+	if a.Wiped() {
+		panic("BUG: tried to use wiped key")
+	}
+	if len(iv) != a.NonceSize() {
+		log.Panicf("Only %d-byte IVs are supported, you passed %d bytes", a.NonceSize(), len(iv))
+	}
+	if len(in) <= tagLen {
+		return nil, fmt.Errorf("stupidChacha20poly1305: input data too short (%d bytes)", len(in))
+	}
+
+	// If the "dst" slice is large enough we can use it as our output buffer
+	outLen := len(in) - tagLen
+	var buf []byte
+	inplace := false
+	if cap(dst)-len(dst) >= outLen {
+		inplace = true
+		buf = dst[len(dst) : len(dst)+outLen]
+	} else {
+		buf = make([]byte, len(in)-tagLen)
+	}
+
+	ciphertext := in[:len(in)-tagLen]
+	tag := in[len(in)-tagLen:]
+
+	res := int(C.openssl_aead_open(a.openSSLEVPCipher,
+		(*C.uchar)(&ciphertext[0]),
+		C.int(len(ciphertext)),
+		(*C.uchar)(&authData[0]),
+		C.int(len(authData)),
+		(*C.uchar)(&tag[0]),
+		C.int(len(tag)),
+		(*C.uchar)(&a.key[0]),
+		C.int(len(a.key)),
+		(*C.uchar)(&iv[0]),
+		C.int(len(iv)),
+		(*C.uchar)(&buf[0]),
+		C.int(len(buf))))
+
+	if res < 0 {
+		return nil, ErrAuth
+	}
+	if res != outLen {
+		log.Panicf("unexpected length %d", res)
+	}
+
+	if inplace {
+		return dst[:len(dst)+outLen], nil
+	}
+	return append(dst, buf...), nil
+}