203 lines
9.2 KiB
Bash
Executable file
203 lines
9.2 KiB
Bash
Executable file
#!/bin/sh
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# Sign with a key held in an HSM, through PKCS#11.
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#
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# hsm-sign detached IN OUT a detached signature of IN (RSA PKCS#1 v1.5 over
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# SHA-256), written to OUT
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# hsm-sign apk IN.apk OUT.apk sign an APK (signature schemes v2 and v3), then verify
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# hsm-sign make-cert SUBJECT setup for apk: a self-signed certificate for the key,
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# signed on the token, written to it beside the key,
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# read back, and printed as PEM. Refuses if the key
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# already has a certificate, unless REPLACE_CERT=1
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# hsm-sign list what Java sees on the token, for diagnosing an alias
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#
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# Environment:
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# PKCS11_PIN the user PIN (required)
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# PKCS11_MODULE the PKCS#11 library; default: opensc's
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# PKCS11_SLOT_INDEX which slot, by position in the slot list; default 0
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# KEY_ID the key's CKA_ID in hex; default 03
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# KEY_LABEL the label make-cert gives the certificate; default apk-cert
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# KEY_ALIAS which key apksigner uses, when the token holds more than one
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# APK_CERT_SHA256 apk: the certificate the APK must be signed with (the SHA-256 of
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# its DER, as make-cert and apk print it); any other is an error
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# REPLACE_CERT make-cert: 1 to replace an existing certificate
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#
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# Why apk needs a certificate on the token: an APK signature embeds the signer's
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# certificate, and Java's PKCS#11 key store only offers a private key that has a
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# certificate with the same CKA_ID. Whatever certificate is there is used, whether
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# make-cert wrote it or not. Android pins an app to its signing certificate for good,
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# so it is chosen once and kept (and pinned with APK_CERT_SHA256).
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set -eu
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die() {
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echo "hsm-sign: $*" >&2
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exit 1
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}
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[ -n "${PKCS11_PIN:-}" ] || die "PKCS11_PIN is not set"
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module="${PKCS11_MODULE:-$(find /usr/lib -name opensc-pkcs11.so | head -n 1)}"
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[ -f "$module" ] || die "no PKCS#11 module at '$module'"
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slot_index="${PKCS11_SLOT_INDEX:-0}"
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# Lower case and an even number of digits, as pkcs11-tool lists ids and as the pkcs11:
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# URI below needs them.
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key_id="$(printf '%s' "${KEY_ID:-03}" | tr 'A-F' 'a-f')"
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[ $((${#key_id} % 2)) -eq 0 ] || key_id="0${key_id}"
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work="$(mktemp -d)"
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trap 'rm -rf "$work"' EXIT
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chmod 700 "$work"
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# The certificate for the key, in DER, to $1; fails if there is none. Certificates are
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# public objects: no login.
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read_cert() {
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pkcs11-tool --module "$module" --slot-index "$slot_index" \
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--read-object --type cert --id "$key_id" --output-file "$1" >/dev/null 2>&1 && [ -s "$1" ]
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}
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# How many certificates the token holds for the key.
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cert_count() {
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pkcs11-tool --module "$module" --slot-index "$slot_index" --list-objects --type cert 2>/dev/null |
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grep -cE "^ *ID: *${key_id}\$" || true
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}
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# A certificate (DER, $1) as a person and as apk_cert_sha256 want to see it.
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describe_cert() {
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openssl x509 -inform DER -in "$1" -noout -subject -startdate -enddate
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echo "sha256 (apk_cert_sha256): $(sha256sum "$1" | cut -d' ' -f1)"
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}
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# SunPKCS11's configuration: which library, which slot.
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cat > "$work/pkcs11.cfg" <<EOF
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name = HSM
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library = $module
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slotListIndex = $slot_index
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EOF
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# What apksigner and keytool need to reach the token through Java. The PIN goes by
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# environment variable name, never on a command line.
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java_store() {
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printf '%s\n' -storetype PKCS11 -providerClass sun.security.pkcs11.SunPKCS11 \
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-providerArg "$work/pkcs11.cfg"
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}
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# apksigner's --provider-class instantiates the provider by reflection, which the module
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# system refuses for SunPKCS11 on Java 9 and later. The JDK's own list of providers
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# already names SunPKCS11, unconfigured; this points that same entry at the token, so
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# the provider is installed by the JVM and apksigner only has to ask for a PKCS11 store.
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java_security() {
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conf="$(dirname "$(dirname "$(readlink -f "$(command -v java)")")")/conf/security/java.security"
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entry="$(grep -o '^security\.provider\.[0-9]*=SunPKCS11' "$conf" | cut -d= -f1)" ||
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die "no SunPKCS11 entry in $conf"
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printf '%s=SunPKCS11 %s\n' "$entry" "$work/pkcs11.cfg" > "$work/java.security"
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echo "-Djava.security.properties=$work/java.security"
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}
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case "${1:-}" in
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detached)
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[ $# -eq 3 ] || die "usage: hsm-sign detached IN OUT"
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# The signature action-hsm-sign has always made, so signatures verify (and match
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# sigstore entries) the same across versions: PKCS#1 v1.5 is deterministic.
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pkcs11-tool --module "$module" --slot-index "$slot_index" --login --pin env:PKCS11_PIN \
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--sign --id "$key_id" --mechanism SHA256-RSA-PKCS --input-file "$2" --output-file "$3"
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;;
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apk)
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[ $# -eq 3 ] || die "usage: hsm-sign apk IN.apk OUT.apk"
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set -- "$2" "$3"
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alias_args=""
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[ -n "${KEY_ALIAS:-}" ] && alias_args="--ks-key-alias ${KEY_ALIAS}"
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# shellcheck disable=SC2086 # alias_args is two words or none, by construction
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JAVA_TOOL_OPTIONS="$(java_security)" apksigner sign \
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--ks NONE --ks-type PKCS11 --ks-pass env:PKCS11_PIN \
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$alias_args \
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--in "$1" --out "$2"
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# Proof, in the log, of what was signed and by whom.
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verified="$(apksigner verify --verbose --print-certs "$2")"
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echo "$verified"
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signers="$(echo "$verified" | sed -n 's/^Number of signers: //p')"
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[ "$signers" = 1 ] || die "expected 1 signer, apksigner reports '${signers}'"
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got="$(echo "$verified" | sed -n 's/^Signer #1 certificate SHA-256 digest: //p')"
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echo "hsm-sign: signed with the certificate whose sha256 (apk_cert_sha256) is ${got}"
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# The certificate is the app's identity: with APK_CERT_SHA256 set, an APK signed
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# with any other certificate (one replaced on the token, a second key) is an error,
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# not an update every installed copy refuses.
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if [ -n "${APK_CERT_SHA256:-}" ]; then
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want="$(printf '%s' "${APK_CERT_SHA256}" | tr -d ': ' | tr 'A-F' 'a-f')"
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if [ "$got" != "$want" ]; then
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rm -f "$2"
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die "the APK was signed with certificate ${got}, not the expected ${want} (APK_CERT_SHA256)"
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fi
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echo "hsm-sign: that is the expected certificate"
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fi
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;;
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make-cert)
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[ $# -eq 2 ] || die "usage: hsm-sign make-cert '/CN=...'"
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subject="$2"
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# The certificate is the app's identity on every device that installs an APK signed
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# with it, so an existing one is not replaced by accident: it is shown, and kept,
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# unless REPLACE_CERT=1.
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if read_cert "$work/old.der"; then
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echo "hsm-sign: key ${key_id} already has a certificate:" >&2
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describe_cert "$work/old.der" >&2
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openssl x509 -inform DER -in "$work/old.der" >&2
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[ "${REPLACE_CERT:-}" = 1 ] ||
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die "not replacing it. Set REPLACE_CERT=1 to replace it (keep the PEM above if anything uses it)"
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echo "hsm-sign: REPLACE_CERT=1: replacing it" >&2
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replacing=1
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else
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replacing=0
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fi
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# OpenSSL's PKCS#11 engine, pointed at the same module, signs the certificate with
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# the HSM's key. The PIN is in a file only this process can read, not an argument.
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cat > "$work/openssl.cnf" <<EOF
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openssl_conf = conf
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[conf]
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engines = engines
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[engines]
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pkcs11 = p11
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[p11]
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engine_id = pkcs11
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MODULE_PATH = $module
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PIN = $PKCS11_PIN
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init = 0
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[req]
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distinguished_name = dn
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[dn]
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EOF
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uri_id="$(printf '%s' "$key_id" | sed 's/../%&/g')"
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# Thirty years: the certificate's dates are not checked for APK signatures, and
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# replacing it would mean a new app identity on every device. Also long enough for
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# Google Play, which wants validity past 2033-10-22.
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OPENSSL_CONF="$work/openssl.cnf" openssl req -new -x509 -sha256 -days 10950 \
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-subj "$subject" -engine pkcs11 -keyform engine \
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-key "pkcs11:id=${uri_id};type=private" -out "$work/cert.pem"
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openssl x509 -in "$work/cert.pem" -outform DER -out "$work/cert.der"
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if [ "$replacing" = 1 ]; then
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# Removed first, so tokens that keep several objects with one id do not end up
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# with two certificates. Cards with one certificate per key may refuse; the
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# write below then replaces it, and the check after it says whether that worked.
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pkcs11-tool --module "$module" --slot-index "$slot_index" --login --pin env:PKCS11_PIN \
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--delete-object --type cert --id "$key_id" >&2 ||
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echo "hsm-sign: could not delete the old certificate; writing over it" >&2
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fi
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pkcs11-tool --module "$module" --slot-index "$slot_index" --login --pin env:PKCS11_PIN \
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--write-object "$work/cert.der" --type cert --id "$key_id" --label "${KEY_LABEL:-apk-cert}" >&2
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# Read back: exactly one certificate for the key, and it is the new one.
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count="$(cert_count)"
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[ "$count" = 1 ] || die "the token has ${count} certificates for key ${key_id} after writing, expected 1"
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read_cert "$work/check.der" || die "could not read the certificate back"
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cmp -s "$work/cert.der" "$work/check.der" ||
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die "the certificate read back is not the one written"
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echo "hsm-sign: written and read back:" >&2
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describe_cert "$work/cert.der" >&2
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cat "$work/cert.pem"
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;;
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list)
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# shellcheck disable=SC2046 # java_store prints one argument per line
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keytool -list -v -storepass:env PKCS11_PIN -keystore NONE $(java_store)
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;;
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*)
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die "usage: hsm-sign detached IN OUT | apk IN OUT | make-cert SUBJECT | list"
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;;
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esac
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